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COMPARISION OF COLD SPRAY GASES, PART 3 of 3

2012-02-06T04:39:15Z

Although the cost of helium can be an order of magnitude higher than that of nitrogen, in a production setting, the option of installing a helium recovery system (HRS) can greatly reduce this cost[i]. Several presenters at the 1^st North American Cold Spray Conference revealed very enlightening facts regarding the ramifications of gas selection. For instance, one speaker from a company that designs and manufactures products and services related to process control and flow measurement provided cost analyses of using helium (with HRS) and nitrogen for a specific application, namely spraying titanium for sputtering target application[ii]. This speaker indicated there is a lower gas cost when using helium with a recovery system ($150/h) compared to using nitrogen ($200/h). He also identified the following advantages obtained when using helium:

· 4.5 Times feed rate when spraying Ti for same coating density.
· > 75 % higher parts processing rate;
· Higher spray temperature capability, thereby reducing the flow rate;
· Lower Porosity Deposits.

Moreover, according to this presenter, the cost of spraying sputtering target with He was calculated to be $360/piece versus $ 2160/piece with N2. In addition, the He process had the advantage of reductions in labor and equipment use.

Filtration & gas separation unit of a helium recovery system[iii].

During the same conference, ARL also provided some valuable findings and recommendations based on their extensive experience using cold spray processing[iv]. These include the following:

. Nitrogen should be used when spraying low cost materials;

. Helium should be used when spraying high value materials;

. The highest possible feed rate will produce improved results;

. Powder characteristics (sizing, morphology etc) are the factor with the largest influence on cost;

. Powders with small diameter particles are preferable;

. A narrow particle size distribution (small SD) is preferable;

. Irregularly shaped particles perform better than spherical;

. Overall coating costs are composed mainly of gas and powder costs;

. These cost calculations do not consider coating quality;

. Helium recycle, not considered here, would lower costs.

REFERENCES

[i] J.-G. Legoux, E. Irissou, s. Desaulniers, J. Bobyn, B. Harvey, W. Wong, E. Gagnon, S. Yue, Characterization and performance evaluation of a helium recovery system designed for cold spraying, International Thermal Spray Conference and Exposition 2010, Thermal Spray: Global Solutions for Future Application (DVS-ASM), pp. 560-565

[ii] S. Desaulniers, Economics of spraying with light gas, North American Cold Spray Conference 2011 – oral presentation

[iii] S. Desaulniers, Helium Recovery System designed for Cold Spraying, 2^nd Canadian Cold Spray Conference 2010 – oral presentation

[iv] D. Helfrtch, M. Trexler, How Operating Parameters and Powder Characteristics Affect Cold Spray Costs, North American Cold Spray Conference 2011 – oral presentation

COMPARISION OF COLD SPRAY GASES, PART 2 of 3

2012-01-24T14:05:18Z

Corrosion studies on cold sprayed coatings using helium and nitrogen yielded some interesting results. In one of the studies, 1100 Al was cold sprayed onto 1100 Al substrates using helium-only and helium-nitrogen mixtureⁱ^[i]. As expected, the coating derived using helium-only gas possessed lower porosity and greater plastic deformation. Ironically, this denser coating possessed lower immersion corrosion resistance compared to the coating derived using helium-nitrogen gas. The authors attribute this lower corrosion resistance to higher residual stress instilled within the coating structure, when forming the dense coating, leading to more active corrosion. In addition, cold sprayed coatings, irrespective of which gas was used, fared better against corrosion when compared to that of 1100 Al substrate.

In a separate study[ii], salt fog testing (35 ºC with 5% salt solution) of cold sprayed Al on Mg using helium and nitrogen led to performances exceeding the minimum acceptance requirement for the application of 336 h. Due to experimental development challenges, this study could not provide a direct corrosion resistance comparison between coatings derived using helium and nitrogen. However, this study did reveal that adherent, dense coatings that provide adequate corrosion protection for some applications can be achieved by cold spray process.

Al-coated Mg panels after exposure in salt fog chamber.

In another study[iii] conducting preliminary work on the mechanical properties of cold sprayed CP-Al on Al 7075-T6 using helium and nitrogen gases, it was shown that the ultimate tensile strengths of both as-sprayed coatings were similar to the strength of the substrate, although the samples derived using nitrogen possessed slightly higher values. The researchers also noted that there may be a velocity regime where the cold spray process imparts beneficial compressive stresses but above which surface damage may occur, thereby reducing the fatigue performance of the coated samples. The bend test results showed that cold spray samples using nitrogen did not result in coating cracks, whereas, cracks were observed on the samples using helium. The preliminary results from this study suggest caution in assuming that all coatings properties will benefit from increased particle velocities. More work in this area is needed to substantiate or refine the interesting results observed in this study.

[i] K. Balani, T. Laha, A. Agarwal, J. Karthikeyan, N. Munroe, Effect of carrier gases on microstructural and electrochemical behavior of cold-sprayed 1100 aluminum coating, Surface & Coatings Technology 195 (2005) pp. 272– 279

[ii] V. K. Champagne, P.F. Leyman, and D. J. Helfritch, Magnesium Repair by Cold Spray, Army Research Laboratory Technical Report 4438 (ARL-TR-4438) May 2008

[iii] J. Barnes, V. Champagne, D. Ballard, T.J. Eden, B. Shoffner, J.K. Potter, and D.E. Wolfe, MECHANICAL AND MICROSTRUCTURAL EFFECTS OF COLD SPRAY ALUMINUM ON Al 7075 USING KINETIC METALLIZATION AND COLD SPRAY PROCESSES, AFRL-ML-WP-TP-2007-431

COMPARISION OF COLD SPRAY GASES, Part 1 of 3

2011-12-19T12:48:28Z

By now most people who have looked into cold spray technology know that the type of propellant/accelerating/process/deposition/carrier gas used in cold spray has an influence on deposit quality. In addition, it is common knowledge that there is a large difference in cost for the two more popular types of process gas used in cold spray, namely nitrogen and helium. This blog will provide insight into some obvious and not-so-obvious differences resulting from the use of these two gases.

Since cold spray relies so heavily on the kinetic energy of the impinging particles, it is important to identify the different means of adjusting this feature. To increase impact velocities of impinging particles, the following measures can be taken: reduce gas molecular weight, increase gas temperature, use longer nozzles for longer stay of particles, and use less-dense and smaller spray particles. Hence, selecting the lower molecular weight helium is an obvious means of attaining higher particle velocities.

Comparison of CP titanium particle velocity profile, in respect to the cold spray nozzle axis, as a function of distance from nozzle exit[i].

Increased particle impingement velocities have been shown to increase hardness[ii]^{, [iii]}, deposition efficiency[iv], adhesive strength[v]^{, [vi]}, and coating densityⁱ^{i, iii, [vii], [viii], [ix], [x]}. These increases are more notable when spraying harder, higher melting temperature powder, such as titanium, which can only be densely cold spray processed using helium gas and not nitrogen^iv,^vii^i,ⁱ^x,^x. For more ductile, lower melting materials, these benefits derived from increased particle velocity are not as prominent. For instance, work carried out by Army Research Laboratory (ARL) on magnesium repair by cold spraying Al alloy^vⁱ shows that spraying with nitrogen gas provides adequate quality for this application.

REFERENCES

[i] S.H. Zahiri, W. Yang, M. Jahedi, Characterization of Cold Spray Titanium Supersonic Jet, Journal of Thermal Spray Technology Volume 18(1) March 2009, pp. 110-117

[ii] K. Balani, T. Laha, A. Agarwal, J. Karthikeyan, N. Munroe, Effect of carrier gases on microstructural and electrochemical behavior of cold-sprayed 1100 aluminum coating, Surface & Coatings Technology 195 (2005) pp. 272– 279

[iv] W. Wong, S. Yue, E. Irissou, J.-G. Legoux, Optimization of Cold Sprayed Pure Titanium, North American Cold Spray Conference 2011 – oral presentation

[v] H. Fukanuma, N. Ohno, A study of adhesive strength of cold spray coatings, Thermal Spray 2004: Advances in Technology and Applications (ASM International) 2004, pp. 329 - 334

[vi] V. K. Champagne, P.F. Leyman, and D. J. Helfritch, Magnesium Repair by Cold Spray, Army Research Laboratory Technical Report 4438 (ARL-TR-4438) May 2008

[vii] S.V. Klinkov, V.F. Kosarev, M. Rein, Cold spray deposition: Significance of particle impact phenomena, Aerospace Science and Technology 9 (2005) pp. 582–591

[viii] S.H. Zahiri, C.I. Antonio, M. Jahedi, Elimination of porosity in directly fabricated titanium via cold gas dynamic spraying, journal of materials processing technology 2 0 9 (2009) pp. 922–929

[ix] W. Wong, E. Irissou, J.-G. Legoux, S. Yue, Influence of helium and nitrogen gases on the properties of cold gas dynamic sprayed pure titanium coatings, http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/ctrl?action=rtdoc&an=16169245&lang=en

[x] J.-G. Legoux, E. Irissou, s. Desaulniers, J. Bobyn, B. Harvey, W. Wong, E. Gagnon, S. Yue, Characterization and performance evaluation of a helium recovery system designed for cold spraying, International Thermal Spray Conference and Exposition 2010, Thermal Spray: Global Solutions for Future Application (DVS-ASM), pp. 560-565

EFFECTS OF CARBIDE SIZE ON CERMET MATERIALS AND COATINGS Part 2: From Bulk to Coating

2011-10-20T06:17:52Z

There have been numerous attempts to transfer these very attractive properties observed in bulk nanostructured WC-Co to coatings. Thermal spray technology has been most commonly used for these attempts. In the first study of its kind, the US Navy work on “Thermal Spray Processing of Nanostructured Coatings”[i] revealed the challenges involved in thermal spraying dense nanostructured WC-Co coatings without excessively decarburizing the nano-scale hard particles. To meet the objective of attaining coatings with intrinsic properties similar to bulk WC-Co, one will have to closely mimic the physical and compositional features of the bulk samples, including reducing excessive decarburization and limiting porosity in the coating. Control and optimization of feedstock (size and structure), selection of thermal spray process, and optimization of process parameters are key components to controlling the microstructure and chemistry of the coating. The following list indicates some of the attributes of thermal sprayed nanostructured carbide cermet coatings compared to their conventional counterparts. (Please note that the author is presenting observed trends; exceptions to the statements can be found on occasion.)

Thermal spray processing of nanostructured carbide cermet feedstock resulted in:

· a coating with greater decarburization[ii]^{, [iii], [iv], [v], [vi], [vii], [viii], [ix]}
· a coating with lower porosity^v^,^vi^{, [x]}
· a coating with more uniform distribution of the hard particles within the metal matrix with a lower mean free path^viii^{, [xi], [xii], [xiii]}
· a coating with higher hardnessⁱⁱ^,ⁱⁱⁱ^,^iv^,^v^,^vi^,^vii^,^viii^{, x,}^xi^,^xii^{, [xiv], [xv]}
· a coating with higher fatigue resistance^xiv
· a coating with higher fracture toughness^xii^,^xv
· a coating with higher abrasive wear resistance (Fig. 1)ⁱⁱⁱ^,^iv^,^v^,^vi^,^xii^{, [xvi]}
· a coating with higher erosive wear resistance^vi^,^x
· a coating with higher sliding wear resistance^viii^{, xi}
· a coating with higher corrosion resistance^viii
· a coating with lower and more consistent friction^{xiii, [xvii]}

Fig. 1: Dependence abrasion resistance on microhardness of conventional and nanostructured WC-Co coatings.^iv

A study by Li et al.^xvi revealed some interesting and very pertinent results. Their findings seemed to indicate that although finer carbides undergo greater levels of decarburization, more of the carbides (whether in original or oxidized stoichiometry) were retained in the coating. The larger carbide particles (> 5 µm) tended to bounce off the surface instead of embedding themselves into the matrix. They also observed that even amongst the larger carbide particles that remained in the splats, the particles were not very well anchored by the matrix. One can then deduce that spraying with finer carbides can lead to improved cohesive and adhesive strength in coating due to enhanced splat-to-splat and splat-to-substrate surface bonding.

Recent studies using cold spray hold promise for advancing the properties of nanostructured carbide cermet coatings by further reducing the process temperature (thereby reducing decarburization) while maintaining the high kinetic energy (thereby decreasing porosity) of the impinging feedstock powder. Kim et al.[xviii] demonstrated the ability to deposit dense nanostructured WC-Co coatings with no signs of thermal degradation (i.e., decarburization) by using cold spray technology. Unfortunately the study did not include any wear test results; however, the coating possessed very high hardness (approx. 2050 HV).

FW Gartner and Perpetual Technologies have carried out their own collaborative work on the development and evaluation of nanostructured WC-Co(Cr) coatings. Syncrude Canada, with their extensive in-house experience in evaluating surface engineered samples, was approached to carry out the abrasion wear test. Their results showed that the nanostructured WC-CoCr coating out-performed all other thermal sprayed WC-Co(Cr) coatings in their database and approached the values observed for welded (plasma transferred arc) deposits with similar chemistries (Fig. 2).

Fig.2: Syncrude Canada’s in-house dry sand rubber wheel abrasion test results comparing nanostructured “multimodal” WC-Co coating against existing coatings of same or similar composition.

REFERENCES

[i] Lawrence T. Kabacoff, “Nanoceramic Coatings Exhibit Much Higher Toughness and Wear Resistance than Conventional Coatings”, The AMPTIAC Newsletter, Spring 2002, Volume 6, Number 1

[ii] D.A. Stewart, P.H. Shipway, and D.G. McCartney, Abrasive wear behavior of conventional and nanocomposite HVOF-sprayed WC-Co coatings, Wear 225-229 (1999) pp. 789-798

[iii] A. Ghabchi, T. Varis, E. Turunen, T. Suhonen, X. Liu, and S.-P. Hannula, Behaviour of HVOF WC-10Co4Cr Coatings with Different Carbide Size in Fine and Coarse Particle Abrasion, Journal of Thermal Spray Technology, Volume 19(1-2) January 2010, pp. 368-377

[iv] M. F. Morks, M. A. Shoeib, A.Ibrahim, Comparative Study of Nanostructured and Conventional WC-Co Coatings, Thermal Spray 2004: Advances in Technology and Applications (ASM International), 2004, pp. 857 – 860

[v] Q. Wang , Z.H. Chen, Z.X. Ding, Performance of abrasive wear of WC-12Co coatings sprayed by HVOF, Tribology International 42 (2009) pp. 1046–1051

[vi] Q. Wang, Z.H. Chen, Z.X. Ding, Z.L. Liu, Performance Study of Abrasive Wear and Erosive Wear of WC-12Co Coatings Sprayed by HVOF, 2008 2^nd IEEE International Nanoelectronics Conference (INEC 2008) pp. 340-344

[vii] P.H. Shipway, D.G. McCartney, T. Sudaprasert, Sliding wear behaviour of conventional and nanostructured HVOF sprayed WC-Co coatings, Wear 259 (2005) pp. 820–827

[viii] J.M. Guilemany, S. Dosta, J. Nin, and J.R. Miguel, Study of the Properties of WC-C Nanostructured Coatings Sprayed by High-Velocity Oxyfuel, Journal of Thermal Spray Technology Volume 14(3) September 2005, pp. 405-413

[ix] J. He, M. Ice, S. Dallek, and E.J. Lavernia, Synthesis of Nanostructured WC-12 Pct Co Coating Using Mechanical Milling and High Velocity Oxygen Fuel Thermal Spraying, METALLURGICAL AND MATERIALS TRANSACTIONS A, VOLUME 31A, FEBRUARY 2000, pp. 541-553

[x] B. Zha, H. Wang, X. Su, Nano Structured WC-12Co Coatings Sprayed by HVO/AF, Thermal Spray 2004: Advances in Technology and Applications (ASM International) 2004, pp. 881-883

[xi] X-Q Zhao, H-D Zhou, J-M Chen, Comparative study of the friction and wear behavior of plasma sprayed conventional and nanostructured WC–12%Co coatings on stainless steel, Materials Science and Engineering A 431 (2006) pp. 290–297

[xii] C. A. da Cunha, N. B. de Lima, J. R. Martinelli, A. H. de Almeida Bressiani, A. G. F. Padial, L. V. Ramanathan, Microstructure and Mechanical Properties of Thermal Sprayed Nanostructured Cr3C2-Ni20Cr Coatings, Materials Research, Vol. 11, No. 2 (2008) pp. 137-143

[xiii] N.I. Smirnov, M.V. Prozhega, N.N. Smirnov, Study of Tribological Properties of Detonation Nanostructured WC-Co-Based Coatings, Journal of Friction and Wear, Vol. 28, No.2 (2007) pp. 200-205

[xiv] A. Ibrahim, C.C. Berndt, Fatigue and Mechanical Properties of Nanostructured WC-Co Coatings, Thermal Spray 2004: Advances in Technology and Applications (ASM International) 2004, pp. 878 – 880

[xv] A. Padial, C.A. Cunha, N.B.Lima, J.R. Martinelli, O.V.Correa and L.V.Ramanathan, STRUCTURE AND PROPERTIES OF THERMAL SPRAYED NANOSTRUCTURED Cr3C2-25(Ni20Cr) COATINGS, 18º CBECiMat - Congresso Brasileiro de Engenharia e Ciência dos Materiais, 24 a 28 de Novembro de 2008, Porto de Galinhas, PE, Brasil.

[xvi] C.-J. Li, Y.-Y. Wang, G.-J. Yang, A. Ohmori and K. A. Khor, Effect of solid carbide particle size on deposition behaviour, microstructure and wear performance of HVOF cermet coatings, Materials Science and Technology September 2004 Vol. 20, pp. 1087-1096

[xvii] X-Q Zhao, H-D Zhou, J-M Chen, Comparative study of the friction and wear behavior of plasma sprayed conventional and nanostructured WC–12%Co coatings on stainless steel, Materials Science and Engineering A 431 (2006) 290–297

[xviii] H-J Kim, C-H Lee, S-Y Hwang, Fabrication of WC–Co coatings by cold spray deposition, Surface & Coatings Technology 191 (2005) pp. 335– 340

EFFECTS OF CARBIDE SIZE ON CERMET MATERIALS AND COATINGS Part 1

2011-10-03T11:25:42Z

Bulk Carbide Cermets

The following blog is a continuation of the blog dated April 21, 2010 entitled, “NANOSTRUCTURED CARBIDE COATINGS - WHY AND HOW?”. Emphasis will be placed on the understanding of how carbide particle size affects the intrinsic properties of bulk nanostructured carbide cermet coatings such as hardness and toughness. Some of the results from the numerous studies attempting to transfer these attractive properties to coating form will be highlighted.

Carbide cermets are also referred to as cemented carbides and represent composite materials that combine very hard carbide particles (e.g., WC, Cr3C2, SiC, TiC, etc.) with a tough metal matrix (e.g., Co, CoCr, Ni, NiCr, etc.). This combination of hardness or strength with toughness makes for a material that is resistant to numerous types of wear. Of the various possible compositions of carbide cermets, WC-Co exceeds all others in terms of application. In bulk form, WC-Co has proven itself to be very valuable for mining and machining tool applications. Since the late 1970s, the trend has been to decrease the carbide size to harness superior hardness and wear resistance.

It is widely accepted that within conventional materials, hardness and toughness are inversely proportional. It is also common knowledge that wear resistance of a material is largely dependent on its hardness and fracture toughness. For conventional carbide cermets, the fracture toughness is a function of mean free path between the carbide particles where the metal binder plastically can deform and tear when subjected to sufficient stress. Hence, one would deduce that uniformly distributed finer carbide particle size should lead to reduced mean free path, thereby reducing the plastic zone and the fracture toughness. On this basis, one would expect the fracture toughness of nanostructured WC-Co to be very low; however, due to the unique physical nature and mechanical properties of nanostructured materials, scientists have observed simultaneous increases in hardness and toughness (Fig. 1) as the carbide particle size is reduced into the nano-scale regime^[i]^{, [ii]}. The improved toughness is likely related to reduction in flaw size, increase in the amount of carbide-matrix interface, and change in the deformation mechanism.

Fig. 1: Surface crack resistance versus hardness of WC-Co materials made using nano, conventional submicron, and commercial WC powders.^[iii]

REFERENCES

[i] K. Jia, T.E. Fischer, B. Gallois, Microstructure, hardness and toughness of nanostructured and conventional WC-Co composites, Nanostructured Materials, Volume 10, Issue 5, July 1998, pp. 875-891

[ii] L. Bartha, P. Atato, A.L. Toth, R. Porat, S. Berger and A. Rosen, Investigation of hip-sintering of nanocrystalline WC/Co powder. Journal of Advanced Materials, 32, 3 (2000), pp. 23–26

[iii] Z. Fang and J.W. Eason, Study of Nanostructured WC-Co Composites, International Journal of Refractory Metals & Hard Materials 13 (1995) pp. 297-303

CARBIDE CERMET COATINGS FOR EROSION-CORROSION APPLICATIONS - STRENGTHS AND WEAKNESSES

2011-09-19T23:09:56Z

Erosion-corrosion is a flow-induced mechanical removal of the protective passivated layer of a metal surface, resulting in a subsequent degradation of the surface through electrochemical or chemical means. The presence of solids or gas bubbles in the fluid can further increase erosion-corrosion. Components used in aircraft gas turbine engines, liquid transports, mineral slurry pipe lines or crude petroleum extraction pumps are exposed to erosion-corrosion type degradation.

Numerous studies and field experience attest to carbide cermet coatings’ ability to resist dry erosion[i]^, [ii]. The combination of high strength/hardness imparted by the carbide particles within a tough matrix of metal results in a resistance to both low- and high-impingement angle erosion. This resistance to both impingement angles is not observed in monolithic materials/coatings. Hence, carbide cermet coatings have been used for protection against erosion-corrosion[iii]^{, [iv]}.

Although carbide cermet coatings with chromium-bearing matrix are often used in corrosion environments, anticipating the level of corrosive degradation within this coating system is not simple. This is due to the fact that corrosive attack occurs at numerous microscopic regions within the carbide-metal composite system[v]^, [vi]. For instance, corrosive attack observed within the carbide particles, at their interfaces (Fig. 1) with the metal matrix, and within the metal matrix is attributed to the fact that the carbide ceramics are electrically conductive and is in intimate contact with a metal matrix with a different electromotive force (emf). Hence, when in the presence of a conductive liquid or electrolyte, the composite system becomes electrochemically active. There are some measures that may address issues relating to corrosion of cermet coatings; these include possibly applying cathodic protection to protect the coating, incorporating non-conductive reinforcement particles (e.g., oxides) in a metal matrix, and/or selecting a metal matrix with high rate of re-passivity.

Fig. 1: Localised corrosion attack around the interface between the hard phase and the matrix after anodic polarization in static 3.5 % NaCl at 18 °C.^v

Anticipating the synergistic effect of erosion-corrosion on carbides may not be trivial. Souza and Neville from the University of Leeds have demonstrated that although the recovery efficiency (ability to re-passivate following surface damage) of super duplex stainless steel is greater than that of HVOF applied WC-CoCr, the latter better resists erosion-corrosion[vii]. The interesting aspect of this result is that both the WC-CoCr and super duplex stainless steel had similar hardness. Hence, in certain conditions, a cermet structure, with what seems to be lower corrosion resistance, may provide superior protection against severe erosion-corrosion applications, compared to a monolithic metal alloy. In a separate study, Neville et al. showed how the relative performance of WC-based MMCs compared to UNS S31603 against erosion-corrosion varied with the size of sand particle size in the slurry[viii]. WC-based MMCs fared better with smaller sand size while UNS S31603 fared better with larger sand size.

Thus, as these findings suggest, it is important to select a material/coating composition and structure that is tailored to the specifics of the erosion-corrosion environment, e.g., erodent size, impinging velocity, solid loading.

REFERENCES

[i] R.C. Tucker, A.A. Ashari, The structure–property relationship of erosion resistant thermal spray coatings, in: C. Codet (Ed.), Proceedings of the 15th International Thermal Spray Conference, Nice, France, May 25–29, 1998, ASM International, 1998, pp. 259–262

[ii] R.J.K. Wood, B.G. Mellor, M.L. Binfield, Sand performance of detonation gun applied tungsten carbide/cobalt–chromium coatings, Wear 211 (1997) pp. 70–83

[iii] Bossong Engineering, “Long Life pump shaft sleeves”, http://bossong.biz/pump_sleeve.htm

[iv] J. Dambrough, Manage Your Assets, Australian Mining, May 26, 2009

[v] V.A.D. Souza and A. Neville, Corrosion and erosion damage mechanisms during erosion–corrosion of WC–Co–Cr cermet coatings, Wear 255 (2003) pp. 146–156

[vi] V.A.D. Souza and A. Neville, Improving lifetimes of pumps, Water & Wastewater Treatment October 2004 page 15

[vii] V.A.D. Souza and A. Neville, Improving lifetimes of pumps, October 2004, http://www.web4water.com/library/view_article.asp?id=2607

[viii] A. Neville, F. Reza, S. Chiovelli, and T. Revega, Erosion-corrosion behavior of WC-based MMCs in liquid-solid slurries, Wear 259 (2005) pp. 181-195

George E. Kim, Ph.D.

F.W. Gartner

Perpetual Technologies, Inc.

email: gkim@perpetualtech.ca

SIMILARITIES AND DIFFERENCES BETWEEN LASER CLADDING AND PLASMA TRANSFERRED ARC PROCESSES

2011-08-31T13:44:14Z

In general terms, cladding can be described as covering one material with another; however, in metalworking terms, cladding can be defined as bonding of dissimilar materials. Within surface engineering, cladding involves the creation of a new surface layer having a different microstructure and/or composition than that of the base material. Amongst the various cladding processes, Plasma Transferred Arc (PTA) and laser cladding have unique and somewhat similar capabilities. Widely accepted characteristics for both of these processes include:

· low energy input;
· low dilution;
· uniform surface finish;
· low porosity;
· little loss of alloying elements; and
· metallurgical bond.

A brief literature search has revealed some differences between the two cladding processes that are worth noting. A number of features favour laser cladding over PTA. For example, laser cladding:

· instils lower energy input which leads to rapid cooling
· produces a finer microstructure
· produces lower dilution[i];
· can provide better surface uniformityⁱ, [ii]; and
· has lower loss of alloying elements[ii].

On the other hand, PTA:

· has lower capital and maintenance costsⁱⁱⁱ;
· has higher thickness capability[i];
· has higher deposition efficiency and rate[ii]; and
· is easier to integrate into some production setting due to small size[ii].

Studies on laser cladded alloys have revealed harder[v] coatings with superior resistance against impact[vi] for Stellite 6, against sliding and/or rolling wearⁱ for Alloy 625, and against corrosion[vii] in NaCl solution for IN-625.

It is interesting to note that the thermal stability of PTA processed Stellite 6 was found to be greater than that processed via laser cladding when exposed to very high temperatures (~ 1,050 ºC)^iv; however, this was not as noticeable when another Co-base alloy was applied by both cladding processes and exposed to temperatures in the range of 700 to 750 ºC[viii].

In recent years, a new laser process has overcome the main challenges associated with previous laser clad technologies. High power diode lasers (HPDL) offer all of the advantages of laser cladding, in addition to lower capital cost, higher electrical efficiency, and smaller size (especially with the fiber delivery option)ⁱⁱ. The introduction of the HPDL has led to new cladding applications, including component refurbishment [ix].

REFERENCES

[i] P.A. Blomquist, Laser Cladding of Alloy 625 for Repair of Aircraft Carrier Catapult Trough Covers, CTMA WORKING SYMPOSIUM, 2002

[ii] Cladding with High Power Diode Lasers, http://www.coherent.com/downloads/CladdingWithHPDDL_WhitepaperFinal.pdf

[iii] R. L. Deuis, J. M. Yellup & C. Subramanian, METAL-MATRIX COMPOSITE COATINGS BY PTA SURFACING, Composites Science and Technology 58 (1998) 299-309

[iv] A.S.C.M. d’Oliveira et al., High temperature behaviour of plasma transferred arc and laser Co-based alloy coatings, Applied Surface Science 201 (2002) 154–160

[v] W.C. Lin, C. Chen, Characteristics of thin surface layers of cobalt-based alloys deposited by laser cladding, Surface & Coatings Technology 200 (2006) 4557–4563

[vi] Shu-Shuo Chang, Hsieh-Chen Wu, and Chun Chen, Impact Wear Resistance of Stellite 6 Hardfaced Valve Seats with Laser Cladding, Materials and Manufacturing Processes, 23: 708–713, 2008

[vii] J. Tuominen, P. Vuoristo, T. Mantyla, J. Latokartano, J. Vihinen, P.H. Andersson, Microstructure and corrosion behavior of high power diode laser deposited Inconel 625 coatings, JOURNAL OF LASER APPLICATIONS, VOLUME 15, NUMBER 1 FEBRUARY 2003

[viii] H. Smolenska, Oxidation and exhaust gas corrosion resistance of the cobalt base clad layers, Journal of Achievements in Materials and Manufacturing Engineering, Volume 31, issue 2, December 2008

[ix] Valdemar Malin, Richard N. Johnson, Federico M. Sciammarella, Laser Cladding Helps Refurbish US Navy Ship Components, DOD AMPTIAC Quarterly Vol.8 no.3, 2004

George E. Kim, Ph.D.

F.W. Gartner

Perpetual Technologies, Inc.

email: gkim@perpetualtech.ca

F.W. Gartner and Harfords Surface Technologies join forces to offer comprehensive Thermal Spray and Laser Cladding services in Australia!

2011-05-25T13:59:07Z

FW Gartner have taken a significant step towards their goal of providing their key clients with global access to cutting edge coating and cladding technology, by signing a contract with Harfords Surface Technologies based in Perth, Western Australia (www.harfords.com.au). Harfords have a long standing reputation for quality and innovation including the introduction of arc spray, HVOF and HVAF processes in their home market. The relationship with FW Gartner will broaden their access to the very latest equipment, technologies, in addition to the all important know-how required to provide their clientele with solutions to their surface engineering and component reclamation needs. Harfords have followed a similar trajectory to FW Gartner in their companies development and also remain a family owned business operating since 1954. In addition to the specific equipment upgrades for laser cladding and other processes introduced by FW Gartner, Harfords are currently upgrading their C.N.C. machining and grinding capacity for expansion and to complement the processes provided by FW Gartner. This agreement is an exciting new chapter for both companies, particularly as Perth becomes a regional base for the global oil and gas industry as well as a one of the pre-eminent mining centers in the world. We welcome an opportunity to discuss the positive implications of having a geographically positioned partner with access to our combined knowledge, equipment, technologies and local contacts to get your job done, how you need it, when you need it and in the way you are familiar with.

FW Gartner with Harfords the right solution at the right time!

"CORROSION PERFORMANCE OF LASER CLAD OVERLAYS AND THERMAL SPRAY COATINGS: A COMPARISON" PART 8 OF 8

2011-05-16T00:58:15Z

Eight part series on the relative effectiveness of laser cladding and HVOF spraying for corrosion resistance. Part 8 of 8

Index of Parts

Introduction
Open circuit potential measurement
Potentiodynamic test
Gravimetric Measurement
SEM
XRD
Vickers
Conclusion

Part 8

Conclusions

This research addresses the comparison study of corrosion resistance characteristics of laser clad and thermal spray coatings. The following are the conclusions drawn:

Laser clad coatings display superior corrosion resistance when compared to HVOF thermal spray coatings.
Microstructure analysis of the SEM images shows that the laser clad coatings contain negligible porosity when compared to thermal spray coatings. This could explain the superior corrosion resistance of laser clad overlays.
Surface morphology analysis of the exposed and unexposed samples during potentiodynamic testing proves that the laser clad coatings remain unchanged whereas thermal spray coatings exhibited significant surface corrosion.
It is evident from the XRD results that both laser clad and thermal spray coatings of SS316 contain both ferrite and austenite phases. The higher percentage of ferrite phase in thermal sprayed coating supports the higher corrosion rate obtained and the SEM images of exposed surfaces during potentiodynamic test (Table 5).
Thermal spray coatings proved to be harder when compared to laser clad coatings. This can be explained by the presence of more oxides in thermal spay coatings.

"CORROSION PERFORMANCE OF LASER CLAD OVERLAYS AND THERMAL SPRAY COATINGS: A COMPARISON" PART 7 OF 8

2011-04-06T01:47:21Z

Eight part series on the relative effectiveness of laser cladding and HVOF spraying for corrosion resistance. Part 7 of 8

Index of Parts

Introduction
Open circuit potential measurement
Potentiodynamic test
Gravimetric Measurement
SEM
XRD
Vickers
Conclusion

Part 7

Microhardness

Microhardness values showed that for each material, thermal spraying results in a harder deposited coating as compared to laser cladding. It is observed that thermal spray coatings are significantly harder than laser clad coatings, which can be explained due to higher oxide content. Among the different materials, irrespective of the method of deposition, Stellite 6 is the hardest coating material, followed by IN-625 and SS316 (Fig 9).

Fig. 9: Average measured microhardness values (HV) for each coating condition

Characterization and Analysis

Microhardness of the coatings was measured on cross sectioned flat samples using a Vickers micro-hardness indenter with a test force of 300 g, and indentation dwell time of 7 seconds. Five indentations were taken for each sample.