Xiaomei Feng

Effects of annealing on Al–Si coating synthesised by mechanical alloying

ABSTRACT An Al–Si composite coating was synthesised on Ti–6Al–4 V alloy substrate by means of mechanical alloying. The as-synthesised coating had a composite structure. The effects of annealing treatment on the microstructure, the mechanical properties and the oxidation resistance of coating were investigated. The increase in annealing temperature was conductive to the formation of multilayered structure of the coating. The formation processes of the layers at different annealing temperatures were discussed. The coating annealed at 800°C had intermetallic layers, which improved the microhardness and wear resistance of the coating. The microhardness of the coating annealed at 800°C reached more than three times of the substrate microhardness. In addition, the coating annealed at 800°C had a thick inner protecting layer, which could retard the inward diffusion of oxygen during oxidation. The annealing of the coating at 800°C could improve the mechanical properties and oxidation resistance of the coating.

Fabrication of Al–Si coating on Ti–6Al–4V substrate by mechanical alloying

ABSTRACT Al–Si coatings were synthesized on Ti–6Al–4V alloy substrate by mechanical alloying with Al–Si powder mixture. The as-prepared coatings had composite structures. The effects of Al–Si ratio, milling duration and rotational speed on the microstructure and oxidation behavior of coating were investigated. The results showed that the continuity and the anti-oxidation properties of the coating were enhanced with the increase of Al–Si weight ratio. The thickness of the coating largely increased in the initial 5-hour milling process and decreased with further milling. A rather long-time ball milling could result in the generation of microdefects in coating, which had an adverse effect on the oxidation resistance of coating. Both the thickness and the roughness of the coating increased with the raise of rotational speed. The low rotational speed would lead to the formation of discontinuous coating. The rotational speed had a limited effect on the coating oxidation behavior. Dense, continuous and high-temperature protective Al–Si coatings could be obtained by mechanical alloying with Al–33.3 wt.%Si powder at the rotational speed ranging from 250 to 350 rpm for 5 h.

Microstructures and properties of Cr–Cu/W–Cu bi-layer composite coatings prepared by mechanical alloying

Abstract Cr–Cu/W–Cu bi-layer coatings with composite structures were fabricated by means of mechanical alloying. The Cr–Cu layer and the W–Cu layer were deposited successively and the as-synthesized bi-layer coating was made up of an inner Cr–Cu layer and an outer W–Cu layer. Microstructures, chemical and phase compositions of the as-prepared coatings were characterized. The results indicated that the bonding between the inner coating and the substrate was improved with the increase of Cu in the raw powder. The annealing treatment of the inner Cr–Cu layer was beneficial to the bonding between the inner Cr–Cu coating and the outer W–Cu coating layer. Mechanical properties such as microhardness, friction and wear resistance were tested. The as-synthesized coating could effectively improve the hardness and wear resistance of the Cu substrate.

Laser cladding composite coating on mild steel using Ni–Cr–Ti–B4C powder

ABSTRACT The composite coating was fabricated by laser cladding on Q235 mild steel. The cross-section morphology, microstructure, phase, micro-hardness and wear resistance of the coating were investigated by scanning electron microscope, energy dispersive spectrometry, X-ray diffraction, Vickers micro-hardness tester and dry sliding wear testing machine, respectively. Results showed that composite coating was gained without cracks and bonded with substrate excellently because of the prominent metallurgical bonding. The composite coating was made up of Ni3Ti, Cr2Ti, Ni–Cr–Fe, TiB2 and TiC. Ceramic reinforcements existed in coating with eutectic and independent structures. The micro-hardness of coating was about 5 times the substrate. Compared with substrate, the coating showed superior wear resistance.

Microstructure and mechanical properties of Ti–Cu amorphous coating synthesized on pure Cu substrate by mechanical alloying method

Mechanical alloying method was applied to fabricate coating with amorphous structure on pure Cu substrate. The microstructure, the phase composition and the mechanical properties including microhardness and wear resistance of the coating were, respectively, characterized and analyzed. The results show that the coating is rough but continuous. It has favorable adhesion to the substrate. The coating is made up of an inner composite layer and an outer amorphous layer. The microhardness and the wear resistance of the pure Cu substrate are improved because of the bilayer structure. The formation mechanism of the coating was discussed. The as-synthesized coating is considered to be effective to strengthen the surface of pure Cu substrate.