Study Of Chemical Mechanical Polishing And The Fabrication Of Nanoindentaion Array Surface Of Titanium Alloy

Titanium alloys process good comprehensive properties, such as high specific strength, corrosion resistance, high temperature resistant, etc., which make it widely used in the field of aerospace, submarine ships, nuclear reactors, weapon, chemical industry, automobile industry nowadays. TA 16 (Ti-2A1-2.5Zr) is a kind of a-titanium alloy which process crystal structure of hexagonal close packing, which was widely used in aerospace engine blades, compressor disk, drum materials and ship valves, pipes and other structure material of nuclear reactor. This paper studies the ultra-precision machining process parameters on titanium alloy surface, and nanoindentation processing of titanium alloy surface preparation of large area, high density of nanotwins in order to improve surface hardness and strength.As the poor processing performance of titanium alloy and it is not easy to get high quality surface, this paper implements ultra-precision machining on the surface of titanium alloy by chemical mechanical polishing and explores the types of polishing pad, abrasive particle size and concentration, concentration of oxidant, pressure and other important factors that affects the results of chemical mechanical polishing of titanium alloy. Finally, suitable polishing pads, compound polishing solution, polishing process parameters are selected, and high quality polished surface was obtained. After grinding, coarse and fine polishing, titanium alloy wafer with surface roughness Ra and PV value of 0.722 nm and 6.061 nm was obtained, respectively.In order to improve the hardness and strength of titanium alloy, quasi static loading method is adopted in this paper. Repeated load was applied on the polished surface of titanium alloy under different load (6 N,5 N,4 N,3N,2 N,1.5 N,1 N,0.5 N) by nanoindentor. According to the analysis, the hardness of titanium alloy surface reaches the highest value under indentation load of 1.5 N.200 cyclic indentation was conducted on the surface of titanium alloy under indentation load of 1.5 N, and then the morphology of indentations was observed by scan electron microscope (SEM). After loading for the first time, the titanium alloy surface hardness value is greatly increased, and the material still processes good plasticity and ductility. Finally, under the indentation load of 1.5 N, macroscopic surface of nanoindentation array was conducted on the surface of titanium and nanotwinned surface was obtained.In order to verify the primary cause of the improvement of hardness of titanium alloy surface is the large amount of twin induced by nanoindentation processing, transmission electron microscopy (TEM) was applied to observe the untreated and conducted titanium alloy by large indentation in this paper. According to the result of characterization, no coherent grain boundary was observed on the titanium alloy surface without indentation processing and selected area electron diffraction (SAED) also present single point diffraction spot. But there are large number of stacking faults and twins after nanoindentation, the coherent twin boundary was observed, electron diffraction shows two point diffraction spot. Due to the accumulation of dislocation and tangles, some small diffraction spots appear in the electron diffraction.