Performance characterization of Ni60-WC coating on steel processed with supersonic laser deposition

Ni60-WC particles are used to improve the wear resistance of hard-facing steel due to their high hardness. An emerging technology that combines laser with cold spraying to deposit the hard-facing coatings is known as supersonic laser deposition. In this study, Ni60-WC is deposited on low-carbon steel using SLD. The microstructure and performance of the coatings are investigated through SEM, optical microscopy, EDS, XRD, microhardness and pin-on-disc wear tests. The experimental results of the coating processed with the optimal parameters are compared to those of the coating deposited using laser cladding.

Towards high-strength cold spray additive manufactured metals:Methods,mechanisms,and properties

Cold spray,as a solid-state additive manufacturing process,has been attracting increasing attention from both scientific and industrial communities.However,cold-sprayed deposits generally have unfavorable mechanical properties in their as-fabricated state compared to conventionally manufactured and fusion-based additive-manufactured counterparts due to the inherent microstructural defects in the deposits(e.g.,porosity and incomplete interparticle bonding).This downside reduces its competitiveness and limits its wide applications as an additive manufacturing process.In the past years,many strengthening technologies have been developed or introduced to adjust the microstructure and improve the mechanical properties of cold-sprayed deposits.The term“strengthening”in this work specifically refers to improving the mechanical strength,particularly the tensile strength of the cold-sprayed bulk deposits.According to the stage that the strengthening technologies are used in the cold spray process,they can be classified into three categories:pre-process(e.g.,powder heat treatment),in-process(e.g.,powder heating,in-situ micro-forging,laser-assisted cold spray),and post-process(e.g.,post heat treatment,hot isostatic pressing,hot rolling,friction stir processing).Therefore,a comprehensive review of these strengthening technolo-gies is conducted to illuminate the possible correlations between the strengthening mechanisms and the resultant deposit microstructures and mechanical properties.This review paper aims to help researchers and engineers well understand the different strengthening methods and provide guidance for the cold spray community to develop new strengthening strategies for future high-quality mass production.

Deposition of FeCoNiCrMn high entropy alloy(HEA) coating via cold spraying

High entropy alloys(HEAs) are of great interest in the community of materials science and engineering due to their unique phase structure. They are constructed with five or more principal alloying elements in equimolar or near-equimolar ratio. Therefore, HEAs can derive their performance from multiple principal elements rather than a single element. In this work, solid-state cold spraying(CS) was applied for the first time to produce FeCoNiCrMn HEA coating. The experimental results confirm that CS can be used to produce a thick HEA coating with low porosity. As a low-temperature deposition process, CS completely retained the HEA phase structure in the coating without any phase transformation. The characterization also reveals that the grains in the CSed HEA coating had experienced significant refinement as compared to those in the as-received HEA powder due the occurrence of dynamic recrystallization at the highly deformed interparticle region. Due to the increased dislocation density and grain boundaries,CSed HEA coating was much harder than the as-received powder. The tribological study shows that the CSed FeCoNiCrMn HEA coating resulted in lower wear rate than laser cladded HEA coatings.

Hardfacing steel with nanostructured coatings of Stellite-6 by supersonic laser deposition

The ability to manufacture coatings is critical to engineering design. Many components require the application of additional layers toenhance mechanical properties and protect against hostile environments. Supersonic laser deposition (SLD) is a novel coating methodbased on cold spray (CS) principles. In this technique, the deposition velocities can be significantly lower than those required foreffective bonding in CS applications. The addition of laser heat energy permits a change in the thermodynamic experience of impactingparticles, thereby offering a greater opportunity for efficient bonding at lower velocities as compared with the CS process. The workreported in this paper demonstrates the ability of the SLD process to deliver hardfacing materials to engineering surfaces. Stellite-6 hasbeen deposited on low-carbon steel tubes over a range of process parameters to establish the appropriate target power and traversespeeds for the coating formation. The coating properties and parameters were examined to determine the primary characteristics andgrain structure size. Their morphology and performance were studied through optical microscopy, scanning electron microscope(SEM), X-ray diffraction, hardness measurements and wear testing. The results have shown that SLD is capable of depositing layers ofStellite-6, with properties that are superior to those of their conventionally manufactured counterparts.

Solid-state additive manufacturing and repairing by cold spraying:A review

High-performance metal additive manufacturing （AM） has been extensively investigated in recent years because of its unique advantages over traditional manufacturing processes. AM has been applied to form complex components of Ti, Fe or Ni alloys. However, for other nonferrous alloys such as AI alloys, Mg alloys and Cu alloys, AM may not be appropriate because of its melting nature during processing by laser, electron beam, and/or arc. Cold spraying （CS） has been widely accepted as a promising solid-state coating technique in last decade for its mass production of high-quality metals and alloys, and/or metal matrix composites coatings. It is now recognized as a useful and powerful tool for AM, but the related research work has just started. This review summarized the literature on the state-of-the-art and problems for CS as an AM and repairing technique.

Solid-state cold spraying of FeCoCrNiMn high-entropy alloy:an insight into microstructure evolution and oxidation behavior at 700-900℃

About 3 mm thick five-element equimolar high-entropy alloy(HEA) FeCoCrNiMn was successfully deposited by solid-state cold spraying(CS).The high-temperature oxidation behavior of the CSed HEA was investigated at 700-900℃.Heat treatment was performed on the CSed HEA before oxidation to heal the incomplete interfaces between the deposited particles.Results show that the microstructure of the CSed HEA is characterized by grain refinement and abundant interparticle incomplete interfaces.Post-spray heat treatment promotes recrystallization and grain growth in the CSed HEA.After oxidation testing,the oxide scales are composed of multi-layers:a Mn_(2)O_(3)(or Mn_(3)O_(4)) outer layer,a Mn-Cr spinel intermediate layer and a Cr_(2)O_(3) inner layer.The CSed HEA exhibits higher parabolic rate constants and more favorable internal oxidation than the bulk HEAs that have similar compositions in the literature.Such a discrepancy becomes pronounced at higher temperatures.The grain refinement and numerous particle boundaries are responsible for such a distinctive performance of the CSed HEA.

New insights into the in-process densification mechanism of cold spray Al coatings: Low deposition efficiency induced densification

This work details new insights into the in-process densification mechanism of cold spray Al coatings. The results show a trend counter to common observations: coating plastic deformation levels and coating density decreases with an increase in particle impact velocity. A lower particle impact velocity and the consequent lower deposition efficiency(DE) results in greater tamping energy per unit volume of deposit,which is the primary reason for the observed trend. This is the first time that DE has been shown to have a non-linear impact on the density of a cold spray coating, with particle in-process tamping being the primary mechanism for coating densification.