This study presents initial findings on three methods for adding carbon to WC-17Co powder to prevent carbide degradation in coatings. The approach had two objectives: first, to saturate the molten cobalt binder with carbon, thereby reducing the dissolution of tungsten carbide; and second, to replace carbon lost during the spraying process, ensuring the final composition could form stoichiometric WC + Co either immediately after spraying or following heat treatment.

This research examines the combination of a corrosion-resistant CoNiCrAlY binder with Cr 3 C 2 carbide particles. The powder was applied using two contrasting thermal conditions: low-energy HVOF and high-energy shrouded plasma spraying. This approach created a wide range of carbide dissolution and peritectic decomposition outcomes. The study includes detailed characterization of the feedstock powder composition to explain the phase formation during sintering compared to the original powder components.

This study examines the development of plasma-sprayed quasicrystalline Al-Cu-Fe coatings with wear-resistant, low-friction, and non-stick properties. Varying hydrogen flow rates during plasma spraying were investigated, revealing that moderate hydrogen addition creates an optimal balance of quasicrystalline phases and oxide formation. These optimized coatings demonstrated superior sliding wear resistance compared to the baseline. Post-treatment by grinding reduced surface roughness, achieving a non-stick surface.

In this research work, MoNbZrTiV and AlNbTaTiV refractory high-entropy alloy (RHEA) material combinations were investigated as potential candidates for feedstock materials for cold spray additive manufacturing. The two RHEA materials as precursors for developing micron-sized particles were alloyed mechanically through high-energy ball milling following a rigorous material design-of-experiments curriculum on account of elemental melting point differences. Detailed particle characterization techniques were employed to gain insights into the RHEA particle properties.

The objective of this work was to explore iron-based green binders as a potential alternative to cobalt-based binders. WC-FeCrNiMo powders with varying particle sizes (fine 25/5 μm and coarse 45/15 μm) were deposited using HVAF spraying with different nozzle configurations. The standard WC-CoCr powder was deposited for comparison. The microstructure and hardness of the deposited coatings were thoroughly analyzed. Performance evaluation included ball-on-disk sliding wear tests, air jet erosion tests, and corrosion tests.

In this study, a high-entropy alloy (HEA) powder containing boron (NiCrCuMoB) was developed for atmospheric plasma spraying to produce coatings with minimal oxide formation in the molten droplets. The in-situ deoxidizing effect of boron during flight was investigated by analyzing collected HEA particles. The oxidation behavior of individual splats deposited on polished stainless-steel substrates was also examined. The resulting coating microstructure and mechanical properties were characterized. The results demonstrate that the addition of boron effectively suppresses in-flight oxidation of the molten particles, leading to the production of HEA particles with low oxide content. Consequently, bulk-like HEA coatings exhibiting strong metallurgical bonding and a reduced oxide content were achieved due to the deoxidizing action of boron.

The metallic bond coat is generally utilized to increase the coating adhesion and the adhesion of thermal spray bond coat is of essential importance to applications. However, it usually depends on mechanical bonding with a low adhesive strength. In this study, a novel metal bond coat with high cohesion strength is proposed by plasma-spraying Mo-clad Ni-based or Fe-based spherical powder particles. Mo-cladding ensures the heating of spray particles to a high temperature higher than the melting point of Mo and prevents metal core from oxidation during spraying. Theoretical analysis on the splatsubstrate/ splat interface temperature and experimental examination into coating-substrate interface microstructure were performed to reveal the metallurgical bonding formation mechanism. The local melting of substrate surface and resultant bond coating by impacting high temperature droplets creates metallurgical bonding throughout the interfaces between substrate and bond coat, and within bond coat. The experiments were conducted with different substrates in different surface processing conditions including Ni-based alloy, stainless steel and low carbon steel. All pull-off tests yielded strong adhesion higher than the adhesives strength of 80 MPa. The present results revealed that Mo-clad metal powders can be used as new bond coat materials and high performance bond coat can be deposited by atmospheric plasma spraying.

Hybrid plasma spraying has been proved to provide novel coating microstructures as a result of the simultaneous injection of a dry coarse powder and a liquid feedstock into the plasma jet. Such microstructure contains both large splats originating from the conventional dry powder and finely dispersed miniature splats deposited from the liquid. This approach enables preparation of coatings from virtually all materials which are conventionally processed using plasma spraying. However, incorporation of materials susceptible to decomposition at high temperatures is still challenging even using this concept due to the high thermal energy provided to all feedstocks to be deposited. Hereby, we propose an innovative approach of incorporation of thermally-sensitive materials into a coating sprayed using a high-enthalpy plasma torch. As a case study, Al 2 O 3 was sprayed from dry coarse powder and MoS 2 was sprayed from the suspension which was deposited directly onto the substrates, i.e., by-passing the hot plasma jet. The retention of the added material in the coating was evaluated using scanning electron microscopy and X-ray diffraction.

In the current work, a NiCrAlY and Fe-based alloy are HVOF-sprayed due to the combination of high coating density and customizable coating properties. The oxygen to fuel gas ratio was varied to modify coating defects in a targeted manner. The results demonstrate material dependent defect mechanisms. Further investigations regarded residual stresses, hardness, and electrical conductivity. In particular, the thermal diffusivity proved to be very promising. Moreover, the coatings were compared with previous work on arc-sprayed coatings of similar chemical composition regarding insulation capability.

Ni/Co-based alloys have been widely employed as bond coats (BCs) in thermal barrier coatings (TBCs) to provide oxidation resistance through the formation of a dense thermally grown oxide (TGO) layer. TGO thickening is a major contributor to TBC failure. Conventional approaches to minimize its growth have included refinement/optimization of the BC composition, deposition techniques, and post-treatments. However, these approaches have only led to incremental improvements in TBC performance and do not directly address the effect of the thin interfacial oxide layer on the TBC lifetime. In a shift from conventional thinking, the development of an Al 4 C 3 -Ni alloy composite BC aims to overcome the challenges generated by current TGOs. Post-deposition heat treatment tailors the coating microstructure to form a continuous internal carbide network. At elevated temperatures, the Al 4 C 3 preferentially oxidizes to form an interlacing protective Al 2 O 3 “root” that provides better TGO anchoring and reduces TBC thermal mismatch with the substrate. In this paper, the coatings were manufactured through gas-shrouded plasma spraying using various parameters to optimize the degree of inflight carbide dissolution and minimize the extent of coating porosity and cracking. XRD and carbon analysis were performed on the coatings and the microstructure was observed using SEM. Differences between coatings are discussed in relation to the spraying parameters.

Conventionally, bulk WC and Cr 3 C 2 -based carbide compositions have been used independently of each other. However, recent investigations have begun to explore combining these carbides together within the same composite/hardmetal coating system. This research builds on earlier work characterising 42%wt% WC-42%wt% Cr 3 C 2 - 16%wt% Ni coatings sprayed under “low”, “medium” and “high” thermal input conditions, to assess their compositions and microstructures after heat treatment in air at 900°C for up to 30 days. Coatings were deposited by HVOF, Ar-He and Ar- H 2 shrouded plasmas respectively, onto Alloy 625 substrates with Ni20Cr bond-coats and top-coats. The coating compositions and lattice parameters were quantified by Rietveld peak fitting of XRD patterns. The microstructures were analysed from cross sectional backscatter electron micrographs. Rapid phase development occurred within the first five days, beyond which the compositions and microstructures remained stable. The microstructures retained extremely fine, sub-micron grain sizes, while the carbide phases exhibited high degrees of metastable alloying, even after 30 days at 900°C. The coating compositions are discussed, and a mechanism proposed to account for the rate of development and overall metastable microstructure.

In this study, Al 2 O 3 -based coatings with varying TiO 2 contents (0, 3, 13, and 40%) were fabricated using atmospheric plasma spraying technique. To compare the superiority of the samples, their thermal properties (thermal conductivity and thermal shock resistance) were characterized. As observed, Al 2 O 3 - 40%TiO 2 (A-40T) coating exhibited relatively superior thermal insulation and thermal shock resistance at 600°C. According to the microstructure and phase analysis, this finding can be attributed to the special phase, Al 2 TiO 5 , and the pre-existing microcracks inside the coating. Thus, A-40T manifested excellent characteristics for thermal insulation application compared with pure Al 2 O 3 and low-TiO 2 content coatings.

There are several challenges when designing components exposed to harsh environments. Cases such as hydraulic turbines and marine propellers are classic examples of demands for materials capable of withstanding erosion and corrosion wear. To enhance and recover worn surfaces, it is usual the use of coatings. This study proposes a new series of coatings based on diffusional effects observed for thermally sprayed chromium carbide coating. A columnar morphology was observed, due to the diffusional gradient perpendicular to the surface. The coating has also shown an absence of porosity and peculiar properties.