Study On Factors To Affect Friction Process With NiTi Shape-memory Alloys

Two important characteristics of Ni Ti shape- memory alloy are shape memory effect and super-elasticity. Its application scope is very wide, such as: aerospace, engineering, electronics, energy, welfare, medicine and etc.Due to shape memory effect and super-elasticity, friction and wear characteristic of Ni Ti alloy is different from that of normal materials. During friction, thermal effect causes martensite transformation, contact stress also causes martensite transformation. Phase transformation not only modifies interface shape, interface energy and etc, but it also changes elastic modulus, Poisson’s ratio, shear modulus, mechanical features. These affect friction system, therefore research on micro and macro aspects of external factors(load, temperature, speed) impacting friction and wear features is very practical.For research on friction and wear feature at macro level, on the basis of Hertz point contact model, establish contact model with a steel sphere sliding on a surface made of Ni Ti shape- memory alloy. The difference of new model is physic-mechanical characteristic of Ni Ti alloy. For normal materials, Hertz point contact model shows that the chart of the stress in contact area is an ellipse, but for Ni Ti alloy, stress chart depends much on temperature and load. Corresponding to each condition of temperature and load, we have one stress chart on the interface. Base on phase transformation temperature and stress-strain chart to define the relationship between load, temperature and characteristic of friction contact area. Then, use molecular mechanical theory to study its friction and wear features. After achieving theoretical orientation, this thesis will perform the experiment by using friction and wear equipment MS-T3000 which has the same operational principles as Hertz point contact model to define friction force and Talorsurf-1000 to measure and define wear amount.At micro level, there are many models to study and calculate friction force on contact surface such as: oscillator model, photon model, electronic emission model, destructive mechanical model and etc. Many scholars have given out different oscillator models such as: independent oscillator model, FK model, FKT model, composite oscillator model, coupled oscillator model and etc. Each of them has its own advantages and disadvantages. On the basis of CO model, the thesis will establish one oscillator model to calculate static friction force and sliding friction force, use this theoretical basis to define input parameters and atomic force microscope AFM to define friction force.Theoretical models will provide us with orienting theory in the research. Experimental result will show us impacting principle of external factors such as load, temperature, speed on micro- and macro- friction and wear. Then we can forecast frictional features, make plans to improve the loss right in the stage of calculating, designing and manufacturing components made of Ni Ti alloy.