In this study, TiB 2 -40Ni and TiB 2 -50Ni powders are deposited on mild steel substrates by HVOF spraying in order to investigate the influence of Ni on coating hardness and corrosion, wear, and thermal shock resistance. The surface morphology and cross-sectional microstructure of the ball-milled powders and composite coatings are examined, and various tests are conducted to measure properties of interest. The findings are presented and discussed in the paper.

This study investigates the effects of feedstock composition and annealing temperature on cold-sprayed aluminum-iron deposits. Commercially available Al and Fe powders mixed in ratios of 55:45, 75:25, and 85:15 were cold sprayed on aluminum substrates, producing dense coatings that were subsequently annealed at 500 and 550 °C. Solid diffusion reactions between Fe and Al produced Al 5 Fe 2 intermetallic compounds, the morphology and content of which were found to depend on annealing temperature and the composition of the as-sprayed deposit. The Fe particles in the Al matrix were fully consumed via compounding reaction with Al at 550 °C. At higher temperatures, however, the intermetallic particles begin to crack possibly due to large tensile stresses.

This study evaluates the effect of annealing on the microstructure, hardness, and wear resistance of FeAl-WC coatings obtained by cold spraying. As-sprayed deposits exhibited a dense microstructure with uniformly dispersed WC particles in the iron matrix. The Fe(Al) solid solution was transformed to an FeAl intermetallic compound at around 650 °C. Further increases in temperature were found to improve the composite microstructure with a slight decrease in microhardness. Wear resistance peaked at 750 °C, and at 950 °C, a diffusion layer appeared at the bottom of the coating close to the substrate.

Nanostructured WC-Co powders were cold sprayed on different substrate materials at different accelerating gas temperatures. Splat morphology and microstructure were examined, showing that the splats are partially embedded in plain carbon and stainless steel substrates with a contour similar to that of the feedstock powder. Gaps and revers were observed around the splats and corrugations or ripples were found on the surface. In contrast, splats on the surface of WC-Co substrates are relatively flat with ejectas on the periphery. A comparison of splats also shows that particle deformation increases with increasing gas temperature and substrate hardness.

The aim of this work is to fabricate a particle-reinforced FeAl composite coating by cold spraying. Fe, Al, and WC powders were placed in a ball mill and mechanically alloyed for up to 36 h in order to obtain a nanostructured Fe(Al) solid solution reinforced with a high volume fraction of WC particles. The powder was examined and then cold sprayed on stainless steel substrates using N 2 as the accelerating gas. The as-sprayed deposits exhibited rough surface morphology and dense cross-sectional microstructure with dual-scale WC dispersoids distributed uniformly in the Fe(Al) matrix. The coatings were annealed at 650 °C and subsequently reexamined. In-situ phase transformation from the solid solution to an intermetallic compound occurred after the post-spray treatment along with an improvement in microstructure.

In this study, Al-SiC composite coatings are produced by cold spraying ball-milled Al powders with different volume fractions of SiC particles. The morphology and microstructure evolution of the powder during ball milling are evaluated along with the effect of SiC content on the microstructure and wear behavior of the coatings. The results show that dense Al-SiC coatings with different volume fractions of SiC particles can be fabricated by cold spraying and that abrasive wear resistance is improved by raising the volume fraction of SiC particles. Wear surfaces indicate that the predominant wear mechanism is gouging of the soft Al matrix in the early stages and cracking and spalling of SiC particles in the latter stages. The dispersed SiC particles serve to protect the matrix from wear products thus raising the wear resistance of the coatings.

In the present study, a nanostructured FeAl coating was prepared by cold spraying of ball milled powder. Annealing treatment was applied to the coating to investigate its effect on the phase structure, grain size and microhardness of the cold-sprayed nanostructured FeAl coating. The results showed that the FeAl phase was kept unchangeable when the coating annealed at the temperature above 500°C. Annealing temperature significantly influenced the microstructure and microhardness of cold-sprayed FeAl coating. With raising annealing temperature, the lamellar structure in the as-sprayed coating disappeared and a dense coating microstructure with fully bonding of deposited particles at their interfaces was achieved after annealing at 950°C. Nanograin growth of the FeAl phase occurred at an annealing temperature higher than 800°C. The microhardness of cold-sprayed FeAl coating remained about 400 Hv 0.1 at the annealing temperature below 800°C and decreased to 300 Hv 0.1 at 1100°C.

In this paper, an iron/aluminum composite coating was prepared by cold spraying using iron and aluminum powder mixture and then annealed to aim at forming iron aluminides by suitable annealing treatment. The annealed coating was characterized using X-ray diffraction (XRD) to determine the coating phases and scanning electron microscope (SEM) with an EDXA energy dispersive spectroscopy (EDS) to examine the coating microstructure evolution. Results showed that the Fe 2 Al 5 intermetallic layer along some regions of the aluminum-iron boundaries forms after annealing at a temperature of 450°C, where true metal to metal contact had occurred. The content of Fe 2 Al 5 phase increased with raising annealing temperature. It was observed that some cracks were developed in Fe 2 Al 5 layer after annealing treatment at a high temperature of 600°C.

For high velocity oxy-fuel (HVOF) sprayed Cr 3 C 2 -NiCr coating, an experimental method to evaluate the carbon and carbide loss of the particles in the stages of both in-flight and impacting on a substrate was proposed. The carbon loss in these two stages was determined by comparing the carbon content in the starting powder, the collected powder sprayed into water and the coating deposited on the substrate. The carbide loss caused by carbide rebounding, dissolving into NiCr matrix and oxidizing in-flight can be determined by evaluating quantitatively the carbide content of the collected powder and the deposited coating. According to the experimental results, it was revealed that the rebounding off of large carbides during particle impact on the substrate is mainly responsible for the carbon loss. The carbide rebounding off and dissolving are two main reasons for the carbide reduction in the coating. The carbon and carbide loss caused by oxidizing during the in-flight of particles is very limited.

HVOF cermet coatings have been widely used to improve the wear resistance. In the present study, an abrasive wear model is proposed according to the examination of wear mechanism. The relation between the relative abrasive wear and the size and content of carbide particles in cermet coating is established. HVOF WC-Co and Cr 3 C 2 -25NiCr coatings are deposited to correlate experimentally the relation between the carbide particle size and abrasive wear. The microstructure of coatings is examined using scanning electron microscopy (SEM). The carbide particle size in the coatings is measured according to SEM images of the coating. It has been found that experimental results correlate with the theoretical model well. The abrasive wear of HVOF carbide cermet coating is determined by carbide size and content. The relative abrasive wear resistance will be increased with an increase in carbide content and the decrease of square root of relative carbide particle size.

The effects of powder types and HVOF spray systems used to produce Cr 3 C 2 -NiCr coating on the relationships between spray parameters and wear performance were investigated based on the effect of fuel gas conditions on abrasive wear and erosion wear. The relationships between spray parameters and wear properties were obtained by orthogonal regression experimental design method. Four types of powders and two HVOF spray systems were used. It is found that with the increase in fuel gas flow or pressure the abrasive wear and erosion of Cr 3 C 2 -NiCr coatings change following a concave curve. The Cr 3 C 2 -NiCr coating with the best wear performance will be deposited under intermediate fuel gas condition. It is experimentally confirmed that by different types of powders and HVOF systems applicable to HVOF spraying of Cr 3 C 2 -NiCr coating, although the optimized fuel gas conditions to deposit coating with the best wear performance will be influenced by types of starting powders.