Powder injection molding （PIM） and die pressing were employed to fabricate nano-TiN modified Ti（C,N）- based cermets. The shrinkage behavior, microstructure, porosity, and mechanical properties of the samples with ...Powder injection molding （PIM） and die pressing were employed to fabricate nano-TiN modified Ti（C,N）- based cermets. The shrinkage behavior, microstructure, porosity, and mechanical properties of the samples with and without nano-TiN addition fabricated by PIM and die pressing were analyzed. It is demonstrated that for either PIM or die pressing, the porosities are obviously reduced, the mechanical properties are significantly improved after adding nano-TiN, and the hard particles are refined; the rim phase thickness obviously becomes thinner, and the number of dimples in fracture also increases. Compared the samples fabricated by die pressing, it is difficult for PIM to obtain dense Ti（C,N）-based cermets. Due to the too much existence of pores and isolated carbon, the mechanical properties of the sintered samples by PIM are inferior to those of the sintered ones by die pressing.展开更多
The paper discussed cutter-work engagement situation hidden behind the mechanical and thermal load effect on cutting edges during high speed hard machining process. The engagement situation was investigated in great d...The paper discussed cutter-work engagement situation hidden behind the mechanical and thermal load effect on cutting edges during high speed hard machining process. The engagement situation was investigated in great detail using experimental and geometrical analytic measures. Experiments were conducted using A1TiN-coated micro-grain carbide end mill cutters to cut hardened die steel. On the basis, a general high speed hard machining strategy, which aimed at eliminating excessive engagement situation during high-speed machining （HSM） hard machining, was proposed. The strategy includes the procedures to identify prone-to-overload areas where excessive engagement situation occurs and then to create a reliable tool path, which has the effect of cutting load reduction to remove the prone-to-overload areas.展开更多
In order to adapt to the high temperature and heavy load process environment of large forgings,a novel die with"fist-like"structure is designed.The“fist-like”die mainly consists of“skin”layer,“bone”lay...In order to adapt to the high temperature and heavy load process environment of large forgings,a novel die with"fist-like"structure is designed.The“fist-like”die mainly consists of“skin”layer,“bone”layer and matrix.To obtain the material with good supportability and good bonding strength with the“skin”layer,iron-based alloys RMD248 and CN72 were selected to make the"bone"layer,and the properties were compared.In this paper,the"bone"layer and the"skin"layer(CHN327)were surfaced on 5CrNiMo matrix by wire arc additive manufacture(WAAM).Then,cyclic heating to 500℃and thermal compression with a maximum deformation of 30%were adapted to test the high temperature mechanical properties.The microstructure changes before and after thermal cycles and compressions were observed by optical microscopy(OM),X-ray diffraction(XRD),energy dispersive spectrometer(EDS)and scanning electron microscopy(SEM).The results show that CN72 has more carbides than RMD248 at the joint surface,which makes it easy to form brittle fracture at the joint.Mechanical properties were tested by using microhardness machine.Meanwhile,hot tensile tests were performed to study bonding strength between the“skin”layer and the“bone”layer.The results show that the RMD248 has stable microhardness distribution while the microhardness of CN72 decreases with the distance from the interface.And the ultimate tensile strength between CN72 and CHN327 is higher than RMD248 in the temperature range of 400-450℃.It can be inferred that CN72 has higher inter-layer wear resistance and RMD248 has more stable high temperature performance.展开更多
基金the National Natural Science Foundation of China (No. 51172018)the Kennametal, Inc. for the fnancial support
文摘Powder injection molding （PIM） and die pressing were employed to fabricate nano-TiN modified Ti（C,N）- based cermets. The shrinkage behavior, microstructure, porosity, and mechanical properties of the samples with and without nano-TiN addition fabricated by PIM and die pressing were analyzed. It is demonstrated that for either PIM or die pressing, the porosities are obviously reduced, the mechanical properties are significantly improved after adding nano-TiN, and the hard particles are refined; the rim phase thickness obviously becomes thinner, and the number of dimples in fracture also increases. Compared the samples fabricated by die pressing, it is difficult for PIM to obtain dense Ti（C,N）-based cermets. Due to the too much existence of pores and isolated carbon, the mechanical properties of the sintered samples by PIM are inferior to those of the sintered ones by die pressing.
文摘The paper discussed cutter-work engagement situation hidden behind the mechanical and thermal load effect on cutting edges during high speed hard machining process. The engagement situation was investigated in great detail using experimental and geometrical analytic measures. Experiments were conducted using A1TiN-coated micro-grain carbide end mill cutters to cut hardened die steel. On the basis, a general high speed hard machining strategy, which aimed at eliminating excessive engagement situation during high-speed machining （HSM） hard machining, was proposed. The strategy includes the procedures to identify prone-to-overload areas where excessive engagement situation occurs and then to create a reliable tool path, which has the effect of cutting load reduction to remove the prone-to-overload areas.
基金National Natural Science Foundation of China(No.51775068)。
文摘In order to adapt to the high temperature and heavy load process environment of large forgings,a novel die with"fist-like"structure is designed.The“fist-like”die mainly consists of“skin”layer,“bone”layer and matrix.To obtain the material with good supportability and good bonding strength with the“skin”layer,iron-based alloys RMD248 and CN72 were selected to make the"bone"layer,and the properties were compared.In this paper,the"bone"layer and the"skin"layer(CHN327)were surfaced on 5CrNiMo matrix by wire arc additive manufacture(WAAM).Then,cyclic heating to 500℃and thermal compression with a maximum deformation of 30%were adapted to test the high temperature mechanical properties.The microstructure changes before and after thermal cycles and compressions were observed by optical microscopy(OM),X-ray diffraction(XRD),energy dispersive spectrometer(EDS)and scanning electron microscopy(SEM).The results show that CN72 has more carbides than RMD248 at the joint surface,which makes it easy to form brittle fracture at the joint.Mechanical properties were tested by using microhardness machine.Meanwhile,hot tensile tests were performed to study bonding strength between the“skin”layer and the“bone”layer.The results show that the RMD248 has stable microhardness distribution while the microhardness of CN72 decreases with the distance from the interface.And the ultimate tensile strength between CN72 and CHN327 is higher than RMD248 in the temperature range of 400-450℃.It can be inferred that CN72 has higher inter-layer wear resistance and RMD248 has more stable high temperature performance.
