The good combination of mechanical and wear properties for cemented carbides is crucial.In this work,the wear behavior of functionally graded cemented carbide(FGCC)and non-graded cemented carbide(CC),with CoNiFeCr mul...The good combination of mechanical and wear properties for cemented carbides is crucial.In this work,the wear behavior of functionally graded cemented carbide(FGCC)and non-graded cemented carbide(CC),with CoNiFeCr multi-principal-element alloy(MPEA)binder,has been investigated by performing sliding wear tests and composition characterization.The results showed that compared with CC,FGCC had higher hardness,stronger fracture toughness,better wear performance,and similar TRS.FGCCs exhibited lower wear rates(3.44×10^(−7)–6.95×10^(−6)mm^(3)/(N m))and coefficients of friction(COFs)(0.27–0.39)than CCs from RT to 600℃due to mitigation of multiple risks caused by binder removal,fragmentation and pull-out of WC grains,high-temperature oxidation and softening.In the low-temperature wear stage,the MPEA binder underwent dynamic recrystallization(DRX)and twinning deformation before removing from the surface.The binder removal caused dislocation pile-ups and stacking faults(SFs)to form under high stress,resulting in fragmentation and pull-out of WC grains.The low-temperature wear was dominated by abrasive wear and adhesive wear,with a low wear rate and a high and unstable COF.In the high-temperature wear stage,initial pitting oxidation of WC grains generated many subgrain boundaries,reducing heat transfer and exacerbating oxidation,resulting in an oxide layer enriched with WO3,Mx Oy,and MWO4.High-temperature wear was dominated by oxidation wear and high-temperature softening,with a high wear rate and a low and smooth COF.The results from the present study do not only provide theoretical guidance for an understanding of the antiwear mechanism of WC-CoNiFeCr,but also a new approach for the preparation of cemented carbides with high wear resistance.展开更多
We present a solver for the Poisson-Boltzmann equation and demonstrate its applicability for biomolecular electrostatics computation.The solver uses a level set framework to represent sharp,complex interfaces in a sim...We present a solver for the Poisson-Boltzmann equation and demonstrate its applicability for biomolecular electrostatics computation.The solver uses a level set framework to represent sharp,complex interfaces in a simple and robust manner.It also uses non-graded,adaptive octree grids which,in comparison to uniform grids,drastically decrease memory usage and runtime without sacrificing accuracy.The basic solver was introduced in earlier works[16,27],and here is extended to address biomolecular systems.First,a novel approach of calculating the solvent excluded and the solvent accessible surfaces is explained;this allows to accurately represent the location of the molecule’s surface.Next,a hybrid finite difference/finite volume approach is presented for discretizing the nonlinear Poisson-Boltzmann equation and enforcing the jump boundary conditions at the interface.Since the interface is implicitly represented by a level set function,imposing the jump boundary conditions is straightforward and efficient.展开更多
基金financially supported by the National Key Research and Development Program of China(No.2021YFB3701800)Special funding support for the Yuelu Mountain National University Science and Technology City“Ranking the Top of the List”Research Project:(Tunnel Boring Machine High-performance Long-life Cutting Tools)the State Key Laboratory of Powder Metallurgy,Central South University,Changsha,China.
文摘The good combination of mechanical and wear properties for cemented carbides is crucial.In this work,the wear behavior of functionally graded cemented carbide(FGCC)and non-graded cemented carbide(CC),with CoNiFeCr multi-principal-element alloy(MPEA)binder,has been investigated by performing sliding wear tests and composition characterization.The results showed that compared with CC,FGCC had higher hardness,stronger fracture toughness,better wear performance,and similar TRS.FGCCs exhibited lower wear rates(3.44×10^(−7)–6.95×10^(−6)mm^(3)/(N m))and coefficients of friction(COFs)(0.27–0.39)than CCs from RT to 600℃due to mitigation of multiple risks caused by binder removal,fragmentation and pull-out of WC grains,high-temperature oxidation and softening.In the low-temperature wear stage,the MPEA binder underwent dynamic recrystallization(DRX)and twinning deformation before removing from the surface.The binder removal caused dislocation pile-ups and stacking faults(SFs)to form under high stress,resulting in fragmentation and pull-out of WC grains.The low-temperature wear was dominated by abrasive wear and adhesive wear,with a low wear rate and a high and unstable COF.In the high-temperature wear stage,initial pitting oxidation of WC grains generated many subgrain boundaries,reducing heat transfer and exacerbating oxidation,resulting in an oxide layer enriched with WO3,Mx Oy,and MWO4.High-temperature wear was dominated by oxidation wear and high-temperature softening,with a high wear rate and a low and smooth COF.The results from the present study do not only provide theoretical guidance for an understanding of the antiwear mechanism of WC-CoNiFeCr,but also a new approach for the preparation of cemented carbides with high wear resistance.
基金supported in part by the W.M.Keck Foundation,by the Institute for Collaborative Biotechnologies through contract no.W911NF-09-D-0001 from the U.S.Army Research Officeby ONR under grant agreement N00014-11-1-0027+1 种基金by the National Science Foundation under grant agreement CHE 1027817by the Department of Energy under grant agreement DE-FG02-08ER15991.
文摘We present a solver for the Poisson-Boltzmann equation and demonstrate its applicability for biomolecular electrostatics computation.The solver uses a level set framework to represent sharp,complex interfaces in a simple and robust manner.It also uses non-graded,adaptive octree grids which,in comparison to uniform grids,drastically decrease memory usage and runtime without sacrificing accuracy.The basic solver was introduced in earlier works[16,27],and here is extended to address biomolecular systems.First,a novel approach of calculating the solvent excluded and the solvent accessible surfaces is explained;this allows to accurately represent the location of the molecule’s surface.Next,a hybrid finite difference/finite volume approach is presented for discretizing the nonlinear Poisson-Boltzmann equation and enforcing the jump boundary conditions at the interface.Since the interface is implicitly represented by a level set function,imposing the jump boundary conditions is straightforward and efficient.
