Study On Microstructures And Tribological Properties Of Cr₃C₂/Ni₃Al Composites Produced By Hot Isostatic Pressing

The main failure mechanism of components in internal combustion engines is the friction and wear behavior.And the wear-resistant performance of the components in the internal combustion engine is directly related to the running behavior of the internal combustion engine.Therefore,developing a wear-resistant material with excellent performance to improve the working efficiency and the service life of internal combustion engine is a scientific problem which should be solved urgently.Cr₃C₂-reinforced Ni₃Al matrix composite is a new type of wear-resistant materials which possess excellent high temperature strength and good wear resistance.Thus,Cr₃C₂/Ni₃Al composites with various Cr₃C₂ contents were prepared using the hot isostatic pressing technique?HIP?in this work.The microstructure,mechanical properties,room-temperature and high-temperature tribological behavor of those materials were also investigated by the scanning electron microscopy?SEM?,energy spectrums?EDS?,X-ray diffraction?XRD?,transmission electron microscopy?TEM?,nanoindentation,Rockwell hardness instrument,tensile testing machine,friction and wear tester and the white light interferometer in this work.The results are expected to provide guiding significance and reference value for the application of Cr₃C₂/Ni₃Al composites in the internal combustion engine.The main results in this work are as follows:?1?The microstructure and phase constitution of the HIP Ni₃Al-alloys and Cr₃C₂/Ni₃Al composites showed that the Ni₃Al-alloys are mainly composed of?'-Ni₃Al and ?-Ni solid solution,and the Cr₃C₂/Ni₃Al composites are mainly constitued with Ni₃Al matrix phase,M7C3?M=Cr,Fe,Ni?diffusion phase and Cr₃C₂ hard core phase.The results indicated that the Cr₃C₂ particles and Ni₃Al powders in the composites have an inter-diffusion during the HIP process.And the Cr₃C₂ particles occur partially decomposed due to the severe diffusion.Finally,the dissolved carbide may to form a more stable M7C3?M=Cr,Fe,Ni?structure during the cooling process.?2?The effects of Cr₃C₂ contents were studied in this study,and results indicated that the hardness instead of the microstructure of the composites is affected by the Cr₃C₂ contents.The phase constitution of the composites is not affected by the Cr₃C₂ contents.However,the macrohardness of Cr₃C₂/Ni₃Al composites and the nano-indentation hardness of their matrix phase are increased as the Cr₃C₂ content increases.Moreover,the strength of the Cr₃C₂/Ni₃Al composites is improved firstly by the addition of Cr₃C₂ particles.But,with the content of Cr₃C₂ particles further increased,the strenght of the Cr₃C₂/Ni₃Al composites is decreased.When the Cr₃C₂ content is increased,the fracture mode of the materials changed from the ductile fracture mode to brittle fracture mode,and the fracture morphology of the Cr₃C₂/Ni₃Al composites from the interpaticle debonding fracture characteristic transformed to the brittle fracture characteristic.?3?The wear mechanism of Ni₃Al-alloys and the Cr₃C₂/Ni₃Al composites under room temperature showed that a work-hardening layer may form firstly under the worn surface of the materials during the wear process;The work-hardening layer may broken down from the worm surface,and then act as hard abrasive particles which cause micro-cutting on the surface of the materials on the following wear process.In the Cr₃C₂/Ni₃Al composites,the carbide strengthening phase may impact the wear behaviors by the following factors:separate the sliding surface,reduce the thickness of the work-hardening layer and block the cutting process of the hard abrasive particles.Therefore,the wear resistance of the composites is increased while the Cr₃C₂ content increases for a certain range of Cr₃C₂ content.But.the excess addition of Cr₃C₂ could result in a decrease in the wear resistance of the composites.Moreover,the gray cast iron counterpart wearing is weakened while the Cr₃C₂ content increases.Therefore,the wear loss of the counterpart gray cast iron decreases as the Cr₃C₂ content is increased.?4?When the temperature is approximately 200 °C',the main wear mechanism of the Cr₃C₂/Ni₃Al composites is abrasive wear and oxidational wear.Under this condition,the optimal Cr₃C₂ addition content is 12 vol%.While the Cr₃C₂ content less than 12 vol.%,the wear resistance of the composites is improved by the Cr₃C₂ addition.However,while the Cr₃C₂ content more than 12 vol.%,the wear resistance of the composites is decreased as the Cr₃C₂ content increases.When the temperature is approximately 350 ?,the main wear mechanism of the Cr₃C₂/Ni Al composites is oxidational wear.And the increase in Cr₃C₂ content led to an increase in the wear loss of the composites,due to the influence of the mechanical property change of the counterpart gray cast iron in 350 0C condition.Under 200 0C and 350 0C temperature,the Cr₃C₂ content increasing benefited to the counterpart gray cast iron in the both cases.In addition,the wear-resistance of the Cr₃C₂/Ni₃AI composites is improved when the temperature change from RT to 350 °C.Meanwhile,the wear-resistance of the counterpart gray cast iron is decreased with the temperature increasing,due to the strength level of the counterpart gray cast iron is reduced.