4V Alloy Substrate Research Articles

MICROSTRUCTURE PERFORMANCE OF La2O3-MODIFIED TUNGSTEN INERT GAS CLAD COMPOSITE COATING

A hard coating free of obvious defects is produced on a Ti–6Al–4V (TC4) alloy substrate by means of tungsten inert gas clad (TIGC) of the Deloro22–WC–La2O3 mixed powders, which greatly increased the surface performance of the substrate. Test results indicated that large quantities of needle-shape precipitates were formed in the Deloro22–WC TIGC coating, increasing the microhardness significantly, and also lots of pores are produced in this coating, weakening the wear resistance. It was noted that a fine/compact microstructure is obtained in the Deloro22–WC–La2O3 TIGC coating, also the defects cannot be observed obviously. La2O3 addition can effectively improve the fluidity of melt and hinder the growth of grains in TIGC pool, favoring a fine/compact microstructure to be produced, and also improving the wear property of the TIGC coating.

Investigation on the Behaviour of Sputter-Deposited Nanocrystalline Cr3Si Film by Double Cathode Glow Discharge

In order to improve the wear resistance and oxidation behaviors of Ti – 6Al – 4V alloy, the sputter-deposited nanocrystalline Cr3Si film was prepared on Ti – 6Al – 4V alloy substrate by double cathode glow discharge. The nanocrystalline film was characterized by using a variety of analytical techniques, such as XRD, SEM, TEM, scratch tester, nanoindentation and Vickers microhardness tester. The phase analysis results showed that the sputter-deposited Cr3Si film (thickness 8µm) was comprised of equiaxed nanocrystalline Cr3Si with a grain size of less than 5 nm. The nanohardness of the nanocrystalline Cr3Si was 2.37 times higher than that of coarse-grained Cr3Si, whereas the elastic modulus of nanocrystalline Cr3Si was approaching to that of coarse-grained Cr3Si. The critical load value obtained by scratch testing of the nanocrystalline Cr3Si film on Ti – 6Al – 4V alloy substrate was 80N, confirming that the nanocrystalline Cr3Si film was well adhered to Ti – 6Al – 4V alloy substrates. Results of cyclic oxidation testing at 700°C and 800°C in air showed that the oxidation kinetic curves of the nanocrystalline Cr3Si film obeyed a parabolic rate law, and oxide scale was mainly comprised of Cr2O3 and amorphous SiO2 with the thickness of < 1µm that could effectively retard the diffusion of oxygen into the nanocrystalline Cr3Si film. The dry wear test results showed that specific wear rate of nanocrystalline Cr3Si film was two order magnitude smaller than that of Ti – 6Al – 4V alloy at RT and 500°C. Keywords: Nanocrystalline Cr3Si, sputter-deposited, high temperature oxidation, wear resistance