Wear Behavior Of Multiphase?VN,Ti B₂-TiC_x?reinforced 7075 Composite Under Different Working Conditions By

Aluminum matrix composites have excellent specific stiffness and specific strength,low thermal expansion coefficient,stable size and excellent wear resistance,so it is widely used in transportation,aerospace,military and national defense fields.Aluminum matrix composites are commonly used in transmission parts under harsh working conditions,such as engine piston.During the piston operation process,the corrosive atmosphere?including SO₂,SO₃,etc.?will be generated by various sulfur,which is one of the constitutions of the diesel oil and lubricating oil.At this time,the wear resistance of aluminum matrix composites become the key factor affecting its use.However,at home and abroad,the research on the wear behavior of piston and other transmission parts mainly focuses on the two working conditions:dry friction and oil lubrication,while in actual service conditions?such as sulfur-containing boundary lubrication?is relatively less.Therefore,this paper not only study the friction and wear properties of aluminum matrix composites under the conditions of dry friction and oil lubrication,but also the condition of sulfur-containing boundary lubrication,and further to comprehend and master the influence of wear conditions on the friction and wear performance of aluminum matrix composites.In this paper,single-phase VN/7075 composite?the content of VN are 5wt.%,10wt.%,15wt.%and 20wt.%,respectively?,two-phase TiB₂-TiC_x/7075 composite?the content of TiB₂-TiC_xare 10wt.%,20wt.%,30wt.%,and 40wt.%,respectively?and multi-phase?VN,TiB₂-TiC_x?/7075 composite are prepared by ball milling and hot pressing sintering,with pure Al7075 as the contrast material.The friction and wear properties of three materials are mainly studied under different working conditions?dry friction,oil lubrication,sulfur-containing boundary lubrication?and different temperatures?room temperature,100?,200??.The wear experiments are carried on MFT-R4000 high-speed reciprocating friction wear tester and HT-1000 high-temperature friction wear tester.The wear surfaces and sub-surface layers of different samples are analyzed by using scanning electron microscopy?SEM?,energy dispersive spectrometer?EDS?,3D laser confocal microscopy,micro-area X-ray diffraction and Raman spectrometer.The effects of working conditions and temperatures on the wear properties of VN,TiB₂-TiC_x/7075 composites are studied.The main conclusions are summarized as follows:The microstructure and mechanical properties of VN,TiB₂-TiC_x/7075 composites show that its mechanical properties firstly increase and then decrease with the increase of VN and TiB₂-TiC_xcontent in single-phase VN/7075 and two-phase TiB₂-TiC_x/7075 composite.When the content of VN is 15wt.%and TiB₂-TiC_xis 20wt.%,respectively,the distribution of VN and TiB₂-TiC_xare more uniform and dispersive in the Al 7075 matrix.The hardness and tensile strength of 15wt.%VN/7075 composites are 119.5Hv and 308.5MPa,respectively,which fracture mechanism is quasi-cleavage fracture.While 20wt.%TiB₂-TiC_x/7075 composites are270.2Hv and 798.7MPa,respectively,and its fracture mechanism is cleavage fracture.The two materials have excellent microstructure and mechanical properties.Under dry friction,oil lubrication and sulfur-containing boundary lubrication,the friction coefficient and wear rate of VN,TiB₂-TiC_x/7075 composites show that dry friction>sulfur boundary lubrication>oil lubrication.Under dry friction,the wear mechanism of Al 7075 is mainly delamination wear,while single-phase 15wt.%VN/7075,two-phase20wt.%TiB₂-TiC_x/7075 and multi-phase?VN,TiB₂-TiC_x?/7075 composites are mainly abrasive wear?micro cutting?,and the wear resistance of multi-phase?VN,TiB₂-TiC_x?/7075 composite is better than other materials in this condition.Under oil lubrication,the wear mechanism of four materials are mainly micro cutting,and the wear resistance of two-phase20wt.%TiB₂-TiC_x/7075 composite is better than that of other materials.Under sulfur-containing boundary lubrication,compare with Al 7075,there are a layer of self-lubricating film?mainly composed of?SN?_xand VS_x?on the wear surface of the composite adding VN,which can improve its wear resistance.The wear mechanism of the four materials are mainly micro cutting,and the wear resistance of multiphase?VN,TiB₂-TiC_x?/7075 composite is better than other materials.The friction and wear properties of VN,TiB₂-TiC_x/7075 composites in different temperatures show that the friction coefficient and wear rate of Al 7075,15wt.%VN/7075 and20wt.%TiB₂-TiC_x/7075 composites increase constantly with the increase of temperature.When the temperature is 200?,the wear rate of 20wt.%TiB₂-TiC_x/7075 composite is 34.0%and its friction coefficient is 5.8%lower than that of Al 7075,respectively,and its main wear mechanism is adhesion and oxidation wear.