| Because of its good biocompatibility, wear and corrosion resistance, superelasticity, high specific strength, Titanium nickel alloy is widely used inbiomedical field. However, there are still two major shortcomings in itsindustrialization process. One is the low hardness. It needs long time servicework once implanted into human body. When subjected to excessive wearhuman tissue can cause human disease. The other is that nickel element itself isa strong carcinogen. The accompanied wear will induce precipitation, cell tissueallergies and poisoning or even cancer response. Many surface modificationmethods are unable to effectively solve the above two factors. Molybdenum hashigh hardness, high temperature strength, strong corrosion resistance, goodmechanical properties and a series of advantages. This paper proposes to use thedouble glow plasma alloying technique to create Mo surface-modified layer inTiNi alloy, which could form metallurgical bonding and composition gradientdistribution diffusion layer to improve the above constraints.Use the double glow plasma alloying technique to create Mo modifiedlayer on the surface of TiNi alloy to study the influence of process parameterson the comprehensive performances of the modified layer. Through the analysis,the optimal technology parameters are: time is2h; pressure is40Pa; sourcevoltage is-550~-700V; cathode voltage is-300~-450V; the source cathodespacing is19mm. Temperature is tentatively set at900degrees and950degrees.X ray diffraction and glow discharge spectroscopy are used to study the phasecomposition and composition distribution of carburized layer. It is not difficultto find the Mo modified layer is mainly composed of Mo, MoTi, MoNi and Ti2Ni phase structure. The cross section elements from the surface to the internalbase present gradient distribution which shows good metallurgical bonding。The hardnesses of Mo alloy surface and cross-section layer are tested byhardness tester and nano indentation test. The results showed900℃and950℃under Mo modified micro hardness layer are respectively832.8HV and762.4HV, which is about3times the hardness of TiNi alloy hardness;cross-sectional microhardness is gradiently distributed, which has a very goodtransitional.Through the reciprocating friction and wear test to study wear resistance ofMo modified layer. Results show that, Mo modified layer treated under900℃shows good antifriction; Mo modified layers have good performance ofwear resisting. Wear resisting performances of Mo modified layers treated under900℃and950℃are3.8times and3.2times as large as the TiNi substrate,respectively. Tests analyse the corrosion resistance of Mo modified layer. Takethe electrochemical reaction after measurement for each10ml to measure theconcentration of Ni+. ICP-MS7500CE mass spectrometry shows that the Ni+concentrations in reaction solution of Mo modified layer treated under900℃and950℃are0.41ppm and0.43ppm, while Ni+concentrations in reactionsolution of TiNi substrate is13.08ppm. Mo modified layers successfully limitNi+release to the human body for a certain degree. |
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