Preparation And Properties Of High Performance,Low Production Cost Double-layer P/M Valve Seats

In recent years,with the continuous improvement of the combination properties of the engine,the traditional forging and casting valve seats are difficult to meet the new demands of the modern high-performance engine,while the single-layer P/M valve seat has a high production cost.Therefore,it is of important economical significance and practical value to develop a high wear resistance,low production cost double-layer P/M valve seat.In this work,orthogonal tests were done to develop a high-performance,low production cost double-layer iron based P/M valve seat,and its properties were studied deeply and systematically.The main research contents are as follows:1.On the basis of the analysis of the material components of the iron based powder metallurgy valve seat for high performance engines,the composition of the high alloy and high performance working layer of the double-layer iron based P/M valve seat is optimized as Fe-1.5C-Cu-2Mo-7Co-1Ni-2Cr,and the composition of the non-working layer is determined as Fe-1.5C-Cu-Ni according to matching level with the coefficient of thermal expansion of the working layer.An ideal interfacial bonding is found between two layers.The material cost of this double-layer valve seat is about 32.6%lower than that of the single layer P/M valve seat which has the same composition.2.The effects of green density and copper infiltration(mass fraction)on the physical properties,mechanical properties as well as the friction and wear properties were studied,the results show that in definite range,with the increase of the amount of infiltration,higher density,hardness and crushing strength of the material are obtained as well as the fretting wear resistance,as the infiltration amount reaches 20%,the mechanical properties and wear resistance of the specimens declined.In addition,higher the green density is,better friction and wear resistance the material has.Friction coefficient,wear volume and wear mechanisms of the working layer change obviously at diffierent temperature,the main wear mechanism of the working layer at room temperature is spalling,and adhesive is main wear mechanism accompanied by abrasive at high temperature.3.Mechining properties of the double-layer material was studies,the results indicate that the order of the effects of turning parameters on the turning temperature is cutting speed>cutting depth>feed rate,while the order of the effects on the the surface roughness is cutting speed>feed rate>cutting depth.The wear mechanisms of the flank face are abrasive,diffusion wear and oxidation wear.While the wear mechanisms of the rake face are diffusion wear and oxidation wear.The breakage mechanisms of the flank face are chipping and fatigue spalling,while the breakage mechanisms of the rake face are fatigue spalling and cracks.Abrupt jumping phenomenon of cutting force F_x,F_y and F_z at the interlayer transition is found when cutting double–layer materials,frequent and sudden change of cutting forces aggravate the tool wear.4.Impact bench test at different temperature was carried out to investgate the combination properties of the double-layer valve seat.The results show that wear conditions of the valve and valve seat are getting worse with the increase of temperature.The surface of the valve seat was worn as plastic deformation failure and fatigue spalling accompanied by slight adhesive when the temperature is 400℃;the valve’s wear mechanisms at 400℃are abrasive,plastic deformation,adhesive and spalling.When the temperature rises up to 600℃,adhesive and plastic deformation failure are getting serious,spalling is also found at the same time.Adhesive wear,pitting and splling of the valve are aggravated at 600℃.