Microstructure And Mechanical Properties Of ZrO₂/Ti Matrix Composites Prepared By Cold Spray-friction Composite Additive Manufacturing

Titanium alloys and their composites are widely used in biomedical fields because of their high specific strength,excellent wear resistance and biocompatibility.The traditional preparation of titanium alloys and their composites has gradually failed to meet the demand for the need of medical titanium alloys and their composites due to the long process and the difficulty of preparing complex and precise structural parts.The rapid development of additive manufacturing has provided a new method and idea for the preparation of complex precision structural titanium alloys and their composites,however,the additive manufacturing technology based on the principle of high temperature melting often suffers from solidification tissue defects and oxidation,which can seriously affect the tissue uniformity and performance of structural parts.To address the defects and shortcomings of the above processes in the preparation of titanium alloys and their composites,this study used a new additive manufacturing method,cold spray-friction stir processing composite additive manufacturing（CFAM）,was applied to successfully prepare monolayer pure titanium and ZrO₂ particle-reinforced titanium matrix composite additive bulks.The microstructure of additive bulks were characterized by using SEM,EBSD and TEM,and evaluated for tensile properties,microhardness and tribological properties.In this study,the organization evolution law of the additive bulks was analyzed,the recrystallization mechanism of the additive bulks was revealed,the tensile fracture damage behavior of the additive bulks was elucidated,and the tribological mechanisms of the additive bulks under different wear environments were analyzed in detail.The results showed that the Ti and ZrO₂/Ti additive bulks prepared by CFAM were dense and uniform,and their densities were increased by 5.4%and 5.6%respectively compared with the Ti and ZrO₂/Ti composite addition bulks prepared by CSAM.In addition,the grain size of CFAM-Ti and CFAM-ZrO₂/Ti additive bulks were more homogenized compared to CSAM-Ti and CSAM-ZrO₂/Ti additive bulks,and the grain size of CFAM-ZrO₂/Ti additive bulk was finer,with the average grain size of CFAM-Ti and CFAM-ZrO₂/Ti additive bulks being 3.1μm and 2.8μm.Both the CFAM-Ti and CFAM-ZrO₂/Ti additive bulks occurred continuous dynamic recrystallization and discontinuous dynamic recrystallization due to the thermal coupling effect of the stirring tool.Particle-induced recrystallization also occurred in the CFAM-ZrO₂/Ti additive bulk.The hardness distribution of CFAM-Ti and CFAM-ZrO₂/Ti additive bulks was uniform,and the average microhardness was 273.1 HV and 485.1 HV respectively,which increased 52.8%and 29.4%compared with CSAM-Ti and CSAM-ZrO₂/Ti additive bulks respectively.This is mainly attributed to the denser CFAM additive bulks and stronger atomic bonding.Compared to the CSAM-Ti and CSAM-ZrO₂/Ti additive bulks,the tensile strength and elongation of the CFAM-Ti and CFAM-ZrO₂/Ti additive bulks were increased by 255%,485%and 256%,18.6%respectively.The tensile fracture of the CFAM-Ti additive bulk showed ductile fracture characteristics,while the tensile fracture of the CFAM-ZrO₂/Ti additive bulk showed mixed ductile and brittle fracture characteristics.Grain strengthening was the main strengthening mechanism of CFAM-Ti and CFAM-ZrO₂/Ti additive bulk.The tribological test results showed that the CFAM-Ti additive bulk had the lowest wear rate and exhibited the best wear resistance in air environment,and the wear mechanisms are abrasive wear and adhesive wear;the CFAM-ZrO₂/Ti additive bulk had the lowest wear rate and exhibited the best wear resistance in SBF environment thanks to the lubrication effect of SBF solution and ZrO₂,and abrasive wear was the main wear mechanism of CFAM-ZrO₂/Ti additive bulk.