The Investigation Of Mechanical Alloying Method To Prepare Amorphous Ti-Cu/Ti-Cu-Al Coatings

In this dissertation, Ti-35Cu (wt%) amorphous coatings on Ti6Al4V (TC4) substrates wereprepared by mechanical alloying. The microstructures, elemental and phase composition ofmechanically alloyed coatings at different milling durations and different milling speed were studiedusing SEM, XRD and EDX. Studies on micro-hardness, friction and wear and adhesion strengthbehavior of the coatings were performed. Influence of5wt%Al in the coating on the coating’sdeposition rate, thickness and performance was also studied. In order to a better understanding themechanism of surface modification of mechanical alloying, the finite element method was used tosimulate some aspects of surface modification of mechanical alloying.It was found that a proper increase in the applied milling time enhanced the densification andnon-crystallization level of the coatings. The coating at a milling time of11h was almost fully denseand amorphous with a thickness of35μm. The inter-diffusion at the coating interface occurred to forma metallurgical bonding between the coatings and the substrates. The micro-hardness from the topsurface to the inner substrate at the section of the coating decreased gradually. It was found that themaximum micro-hardness at the coating surface reached625.5Hv0.1. At a milling time of11h, thefriction coefficient of coating was0.20and the corresponding wear weight loss is0.8mg. Theadhesion strength between the coatings and the substrates was improved with increasing millingdurations and reached the maximum value44.6N at a milling time of11h.At a milling speed of500rpm, the value of coating surface’s micro-hardness is657.4Hv0.1andthe adhesion strength between the coatings and the substrates reached the maximum value47.5N,however the content of amorphous phase in the coating is lower than that of400rpm. Adding5wt%Alelement in the coating improved the coating’s deposition rate greatly. At a milling time of11h, thedensity of Ti-33.3Cu-5Al reached the maximum value and the thickness of the coating is550μm.There is no amorphous phase forming at the interface of the Ti-33.3Cu-5Al coating and substrate,however amorphous phase can be detected at the area near the coating surface.Through finite element analysis, it was found that after repeated hit by the balls the interface ofthe coating and the substrate had a jagged morphology. The accumulated plastic deformation and thetemperature of the substrates increased with the milling speed. The maximum value of the substrate’saccumulated plastic deformation was0.06and the maximum temperature of substrates was85℃. Theresidual stress reached its maximum value at a milling speed of500rpm and the value of compressive stress σzzwas350Mpa.