Microstructure Evolution And Diffusion Behavior In Dry Sliding Friction-induced Deformation Layers Of T10/20CrMnTi Tribopairs

Phenomena such as plastic deformation transformation, defects increase, grainrefinement, as well as elemental diffusion in the tribolayer caused by shear andfrictional heat during friction and wear process severely affect wear resistance ofmaterials and reduce the reliability of the tribo-pairs. Therefore, studies on thestructure and composition evolution of materials during friction and wear process arevery helpful for the design and development of new tribological materials andintelligent recoating as well as improvement in abrasion resistance and reliability.In this study, T10steel and20CrMnTi steel were selected as pins and discsseparately. Aimed at three groups of tribo-pairs including T10steel pin/quenched andtempered20CrMnTi steel disc, quenched and tempered T10steel pin/quenched andtempered20CrMnTi steel disc, quenched and tempered20CrMnTi steel pin/chromized T10steel disc, their dry sliding friction behaviors, the micrographies ofsliding friction induced deformation layers(SFIDL), nanohardnesses and shear stainswere studied separately. Meanwhile, grain refinements, element diffusions and surfacetemperature raises in the SFIDLs were also analysed. The conclusions are as follows:The tribological behaviors of T10and20CrMnTi steel tribo-pairs were studiedunder different experimental conditions. For T10pin/quenched and tempered20CrMnTi disc tribo-pairs, friction coefficient decreased with the increased loads andspeeds, and the tribological performances were both better. Compared with T10pin/quenched and tempered20CrMnTi disc tribo-pairs, the friction coefficient ofquenched and tempered T10pin/quenched and tempered20CrMnTi disc tribo-pairwas more stable, and the wear-resisting performance was also enhanced. Forquenched and tempered20CrMnTi pin/chromized T10disc tribo-pair, the tribologicalperformance was significantly improved.The wear mechanisms of T10and20CrMnTi steel tribo-pairs were studied underdifferent experimental conditions. For T10pin/quenched and tempered20CrMnTidisc tribo-pairs, wear mechanisms of T10were adhesive wear, abrasive wear and oxidation wear, and wear mechanism of20CrMnTi was mainly adhesive wear. Theincreased hardness of quenched and tempered T10resulted in its fracture and part oftheworn surface spalling. The wear mechanism of quenched and tempered20CrMnTipin against chromized T10disc, changed from adhesive+abrasive wear to mainlyadhesion wear. The wear mechanism of chromized T10disc was mainly spalling wear.The SFIDLs morphologies and structures of T10and20CrMnTi steel tribo-pairswere studied under different experimental conditions. For T10pin/quenched andtempered20CrMnTi steel disc tribo-pairs, the SFIDLs of both pin and discwerecomposed of mechanical mixing layers (MMLs) and severe plastic deformationlayers (PDLs). For quenched and tempered T10pin/quenched and tempered20CrMnTi disc tribo-pair, the SFIDLs of both pin and disc were only composed ofsevere plastic deformation layers (PDLs). For quenched and tempered20CrMnTi pin/chromized T10steel disc tribo-pair, there was no SFIDL in T10disc, and the SFIDLof quenched and tempered20CrMnTi was only severe plastic deformation layer(PDL).The nano-hardness and equivalent strain in the SFIDLs were studied. For T10pin/quenched and tempered20CrMnTi disc tribo-pairs, nano hardness decreased withincreased depth from worn surface, and the highest nano-hardness of T10pin is10.36GPa. The equivalent strain gradually reduced with increased depth from wornsurface, and the equivalent strain of T10pin is less than that of20CrMnTi disc,because of its lower hardness. For quenched and tempered T10pin/quenched andtempered20CrMnTi disc tribo-pair, nano hardness of both pin and disc can be dividedinto three layers: the initial hardness of pin is higher than that of disc in the first layer,under the same depth the nano-hardness of pin is less than that of disc in layer2, bothare for matrix hardness in layer3. With increased distance from the worn surface,both pin and disc equivalent strains decreased, and the equivalent strain of pin wasalways larger than that of20CrMnTi. The nano hardness of chromized T10discagainst quenched and tempered20CrMnTi pin was less than that of20CrMnTi pin at0-5μm. The worn surface temperatures of T10pin/quenched and tempered20CrMnTidisc tribo-pairs were studied by ABAQUS finite element simulation, which increased with the increased loads and speeds. The highest worn surface temperature reached374.2℃.Grain refinement and cementite dissolution were studied by TEM observation.For T10pin/quenched and tempered20CrMnTi disc tribo-pairs, cementitefragmented even dissolved and formed the nanocrystals in the worn surfaces of T10pins, and the dislocation density in martensite increased dramatically in the wornsurface of20CrMnTi disc. The forming mechanisms of grain refinement andcementite dissolution were considered to be the joint action of dynamicrecrystallization induced mainly by frictional heat and deformation rather than puresevere shear deformation. For T10pin, the smallest size of grain refinement ferritewas about20nm.Diffusional phenomena between T10pin/quenched and tempered20CrMnTisteel disc tribo-pairs were studied by TEM observation. The SIMS analysis showedthat Cr and Ti elements in mating material diffused into the T10pins SFIDLs, ofwhich depths were5-7μm,10-12μm,25-30μm and7-8μm,10-12μm,14-15μmseparately under the condition of200rpm,40N,50N,60N. Combining with the wornsurface grain size and dislocation density and worn surface temperature rise, diffusioncoefficient fitting formula in MML and PDL could be described as:Compared with the test results, it can describe the atomic diffusion behaviors wellbetween the steel tribo-pairs under the dry sliding friction.