Μm For Powder Research Articles

Optimization of ceramic content in nickel–alumina composite coatings obtained by low pressure cold spraying

The paper describes the technology of nickel-alumina composite coatings obtained by low-pressure cold spray (LPCS). The content of alumina reinforcement was optimized by mixing the commercial K32, being a mechanical mixture of Al2O3 + 50 wt% Ni, with the Ni-cladded alumina powders developed in present study. The cladded powders were prepared by hydrogen reduction method. Two powders including Ni-films covering Al2O3 particles were developed: Al2O3 + 70 wt% Ni (powder # 1) and Al2O3 + 80 wt% Ni (powder # 2). The morphology of obtained cladded powders, analyzed using scanning electron microscope (SEM), showed a porous, cauliflower-like morphology in cladded layer of powder # 1 and dense nickel layer in powder # 2. The measurements of granulometry enabled finding the powder size distribution of pure alumina powder having a mean value of about 50 μm which increased by cladding to about 70 μm in powder # 1 and to about 65 μm in powder # 2. The cladded powders were mixed with K32 powder and sprayed using LCPS onto mild steel substrate. The microstructure of obtained coatings was characterized using SEM, energy dispersive X-ray spectroscopy (EDXS) and electron backscatter diffraction (EBSD). The graphical analysis of coatings' cross-sections enabled determining content of alumina in sprayed deposits. This content increased from about 7% in K32 powder sprayed coatings to 9–13% in coatings obtained using its mixtures with powder # 2 and up to 20–30% for mixtures with powder # 1. The microhardness of coatings sprayed using the mixtures of powder # 1 with powder K32 as well as the coating sprayed only with the powder K32 were slightly greater than HV 0.1 > 150. The microhardnesses of about HV 0.1 ≈ 200 was reached for the coatings sprayed using mixtures of powder # 2 with K32. Finally, the bond strength of the sprayed coatings, measured using test ISO 14916, was in the range from 1.7 to 5.9 MPa. The greatest bond strength was reached for the coatings sprayed using powder K32.

An electrodeposition approach to obtaining carbon nanotubes embedded copper powders for the synthesis of copper matrix composites

CNTs/Cu composite powders were fabricated using an electrodeposition process, and consolidated by hot pressing followed by cold rolling. The electrodeposition is a promising method to obtain homogeneously dispersed CNTs/Cu powders in terms of effective control of CNTs content and particle size of powders during the process. The effects of Cu ions concentration in electrolyte on the dispersion and content of CNTs in powders, particle size, and properties of composites were studied. The electrodeposited CNTs/Cu powders show large amount of embedded CNTs that are strongly bonded with the Cu matrix, and a CNTs network architecture formed in the Cu grains. The particle size 52.72 μm of powders is obtained at Cu ions concentration of 10 g/L in electrolyte. The tensile strength and electrical conductivity of consolidated CNTs/Cu composites are about 418 MPa and more than 90 ± 0.16% IACS, respectively. The CNTs network is beneficial to load transfer efficiency and bridge linking for improving strength, but also provides electron transport pathways for high electrical conductivity.

Preparation and surface properties of cashmere guard hair powders

Cashmere guard hair, a by-product from the cashmere dehairing industry is used for low value applications because the guard hairs are not suitable for spinning as they are coarse, contain large medullation and lack crimp or curvature. To find new uses in high value-added applications, cashmere guard hairs were milled into fine particles using the processing sequence Chopping→Attritor milling→Spray Drying→Air Jet milling. The guard hairs were partially hydrolysed with hydrochloric acid which increased the pulverisation rate due to the deterioration in mechanical properties. The volume median particle size d(0.5) was reduced from 2.328μm, for untreated cashmere guard hair powder to 0.461μm for powder from the acid hydrolysed guard hairs. FTIR and XPS studies revealed the breakdown of the cashmere guard hair cuticle cells and the exposure of the cortex on the powder surface along with the oxidation of the cashmere guard hair during milling.