Research On The Magnetic Pulse Powder Compaction-sintering Mechanism And Performance Of CNTs Reinforced TC4 Composites

TC4 alloy has excellent physical and chemical properties,and is usually applied in the manufacturing of hinge parts such as carrier equipment and medical devices.Due to the difficult cold working characteristics of TC4 alloy,powder compaction technology has become an effective way to solve this problem.As the service environment becomes more and more severe,better physical and chemical properties are required.For the performance enhancements of a certain aspect of the materials,the corresponding metal matrix composites are usually prepared by the powder compaction technology enhanced by the second phase.Multi-walled carbon nanotubes(CNTs)have better elastic modulus,tensile strength and small thermal expansion,and are considered to be one of the most potential reinforcing phases in composites.In this paper,the magnetic pulse high-speed compaction process is proposed to prepare carbon nanotube-reinforced TC4(CNTs/TC4)composites.Taking the CNTs/TC4 powders as the research object,firstly,the magnetic pulse powder compaction platform was built based on the principle of magnetic pulse compaction,and the compaction characteristics of the powder bodies under different compaction parameters were studied.Secondly,the compaction model of the CNTs/TC4 powder bodies was established by numerical simulation method,the deformation behavior and distribution of the powders in the compaction process were analyzed,and the related theoretical relationships of powder compaction were constructed.Subsequently,the sintering properties of CNTs/TC4 compacts under different parameters were explored.Finally,the thermal oxidation failure behavior and wear resistance of CNTs/TC4 composites were comprehensively studied under different working conditions.The main research contents and results of this paper are as follows:(1)The magnetic pulse powder compaction process platform was built to solve the problems of difficult forming and poor compaction performance of the traditional compaction process.Through the built process platform,the change rules of compaction process parameters and relative density,end face micro morphology,compressive strength and fracture morphology were explored.Firstly,the influence of discharge energy and compaction temperature on the compaction characteristics of powder bodies was studied.Finally,the optimal compaction parameters of magnetic pulse powder compaction process were obtained,and the relationship between compact density and compaction temperature was corrected.(2)The electromagnetic field and thermal/structural field models of magnetic pulse powder compaction were established,and the accuracy of the models was verified by the compaction displacement of the punch.Firstly,through the simulation analysis of the models,the distribution law of relative density,equivalent stress and strain during the compaction of the powder bodies was analyzed,and the compaction mechanism of the powders was revealed.Finally,the relationship between the volume strain of the powders and the compaction time,the density was established,and the compaction equation was corrected by the 7-term Gaussian fitting method.Important compaction parameters such as compaction force,velocity,displacement,and density could be predicted through compaction time.(3)The evolution trends of the sintering temperature and the thermal expansion properties,relative density,compressive strength and micro-morphology of the compacts were revealed.Firstly,the influence of sintering temperature on the thermal expansion properties of green compacts was analyzed,and then the variation trend of the sintering properties of the samples at different temperatures was studied.A more suitable sintering temperature was obtained by the test methods of micro-morphology and mechanical properties.The strengthening mechanism of the sintered bodies was revealed.The relationship between the density of the sintered bodies and the relative length was corrected,and the density of the sintered bodies could be effectively predicted by the sintering temperature.(4)The effects of heat treatment time and temperature on the oxidation resistance of the composites were studied,and the Gaussian relationship between the compressive strength and the corresponding strain of the samples as a function of oxidation parameters was obtained.The oxidation kinetic curves of the samples were obtained by oxidation tests,and then the oxidation micro-morphology and phase composition of the sample were analyzed.Finally,the mechanical properties of the samples under different oxidation parameters and the microscopic analysis of the fracture morphology were carried out.A reliable relationship between compressive strength and corresponding strain as a function of oxidation parameters was established,and the influence of oxidation parameters on the oxidation failure behavior of samples was revealed.(5)The influence mechanism of oxidation temperature and normal load on the wear properties of composite samples was revealed.The relationship between oxidation,wear parameters and wear volume was constructed,and the anti-oxidation and wear-resistant strategy under high temperature environment was formulated.Firstly,the friction coefficient and weight loss of the samples were tested under different loading conditions,and the distribution law of friction coefficient and wear rate was obtained.The micro-morphology and elemental composition of the worn surface were analyzed to reveal the change rule and the wear mechanism of the samples.Finally,the relationship between the wear volume and the oxidation temperature,oxidation time,normal load,and wear distance was established.