Heterostructured NiCr matrix composites with high strength and wear resistance

Self-lubricating composites are required to have excellent tribological performances and good mechanical properties when they are applied as mechanic parts.However,the brittle nature of most lubricants will weaken the mechanical properties of the composites where in order to get the lubricating ability proper amount of lubricants are usually incorporated,bringing challenges for them to get well-balanced mechanical and tribological properties.In this study,Ni Cr matrix self-lubricating composites with the addition of WS_(2)and nano-Ti were prepared via spark plasma sintering.The hard phase of Ni_(3)Ti and the lubricant Ti S were formed via in-situ reaction at the interface,which surrounded the soft alloy matrix and developed a heterostructure.Compared with the conventional Ni Cr-WS_(2)composite,the heterostructured composite exhibited a high yield strength of 1645 MPa,a low friction coefficient of 0.37 and a wear rate of as low as 2.25×10^(-5)mm^(3)N^(-1)m^(-1)when sliding.Finite element analysis demonstrated that the heterostructure plays a key role to balance well the mechanical and tribological properties of the Ni Cr matrix composites.

High-entropy FeNiCoCr alloys with improved mechanical and tribological properties by tailoring composition and controlling oxidation

Many metal matrix self-lubricating composites possess excellent comprehensive properties of high strength and wear resistance after incorporating various lubricants that usually belong to ceramic phase.However,this improvement is always obtained at the cost of notable decrease in toughness.In order to break through this toughness-tribological properties trade-off,self-lubricating composite alloys based on the matrix of Fe NiCoCr_(0.5) high entropy alloy(HEA)were prepared by milling addition of element Co or Cr and then spark plasma sintering(SPS).Co or Cr is added into the base HEA with the aim of tailoring oxidation behavior,mechanical properties as well as tribological performances.As no ceramic lubricants are used,the alloy composites remain high toughness.Co or Cr element addition leads to the precipitation of a hard phase of a-Cr and grain refinement,both of which contribute to the increase of mechanical strength.On sliding,oxidation of Fe and Ni is suppressed.Instead,the oxides of cobalt and chromium are formed upon the Co-and Cr-modified HEAs,respectively.These oxidation products,especially the oxides of cobalt that are easy to be sintered on sliding,are in favor of the formation of a lubricating glaze layer at 400℃on the worn surface,and thus the decrease in friction coefficient and wear rate,which are 0.33 and 4.0×10^(-5) mm^(3)/(N m),respectively.

Comparative study of mechanical and wear behavior of Cu/WS_2 composites fabricated by spark plasma sintering and hot pressing

The mechanical and wear behavior of copper-tungsten disulfide（Cu/WS_2） composites fabricated by spark plasma sintering（SPS） and hot pressing（HP） was investigated, comparatively. Results indicated that the addition of lubricant WS_2 substantially reduced wear rate of the Cu matrix composites fabricated by SPS,and the optimum content of WS_2 is 20 wt% with regard to the wear behavior. However, it affected a little to the wear rate while dramatically decreased the friction coefficient of the composite fabricated by HP.This difference in friction behavior of the self-lubricating composites fabricated by the two techniques was closely related to their different mechanical properties. Severe interfacial reaction occurred during spark plasma sintering, leading to brittle phase formation at interface.

Improving high-temperature wear resistance of NiCr matrix self-lubricating composites by controlling oxidation and surface texturing

Self-lubricating composites(SLCs)are widely used in the fields of aerospace and marine,but the conventional NiCr matrix SLCs with sulfide as solid lubricant often suffer from low wear resistance at high temperatures.In view of its high affinity with oxygen and also the high oxidation rate,appropriate amount of nano Ti was added to NiCr-WS_(2)composites prepared by spark plasma sintering(SPS)to adjust the oxidation behavior and surface texture.When exposed to high temperature,Ti was preferentially oxidized in comparison to Ni and Cr,resulting in abundant TiO_(2)protrusions and microdimples on the surface,i.e.in situ surface texturing.Besides,TiO_(2)was of high chemical activity and readily to react with other oxide debris during high temperature sliding process to form compounds of NiTiO_(3)and CrTi_(2)O_(5).The high chemical activity of oxide debris that was conducive to sintering,combining with the special surface texture that stores as many wear debris as possible,promoted the rapid formation of a protective glaze layer on the sliding surface.The NiCr-WS_(2)-Ti composite exhibited low friction coefficient but high wear resistance at elevated temperatures.Especially at 800℃,it presented a wear rate of as low as(2.1±0.3)×10^(-5)mm^3N-1m^(-1),accounting for only 2.7%of that of NiCr-WS_(2)composite.

Effect of Interfacial Microstructure on Mechanical and Tribological Properties of Cu/WS_(2) Self-Iubricating Composites Sintered by Spark Plasma Sintering

In this study,Cu/WS_(2) self-lubricating composites are fabricated by spark plasma sintering.Interfacial microstructure and its effect on mechanical and tribological properties are investigated.High sintering temperature at 850℃promotes decomposition of WS_(2) and its following interfacial reaction with Cu to form Cu_(0.4)W_(0.6) nanoparticles and Cu_(2)S,enhancing mechanical properties as well as wear resistance of the composites.But the destruction of WS_(2) leads to a high friction coefficient.On the contrary,for the composites sintered at 750℃,a nanoscale diffusion zone forms at the Cu/WS_(2) interface.WS_(2) lubricant retains its lamellar structure.The composite shows excellent self-lubrication performance,with a low friction coefficient of 0.16.However,its mechanical properties are low,and the wear rate is one magnitude higher.