Diffusion bonding of AlCoCrFeNi2.1 eutectic high entropy alloy to TiAl alloy

High entropy alloys have special microstructure and remarkable properties.To explore their potential engineering application in high temperature structures,the microstructure evolution of bonding interface,the elemental diffusion behavior and mechanical property of the diffusion bonded joint between AlCoCrFeNi2.1eutectic high entropy alloy(EHEA)and TiAl alloy were investigated.Four reaction layers(rodlike B2 phase,Al(Co,Ni)2Ti,τ3-Al3NiTi2+TiAl,τ3-Al3NiTi2+TiAl+Ti3Al)formed in the diffusion zone near FCC phase of EHEA,but three layers(Al(Co,Ni)2Ti,τ3-Al3Ni Ti2+Ti Al,τ3-Al3Ni Ti2+Ti Al+Ti3Al)formed near B2 phase.Al and Ni controlled the reaction diffusion of EHEA and TiAl alloy,coarsened the acicular precipitated B2 phase and turned Ti Al phase into Al(Co,Ni)2Ti andτ3-Al3NiTi2 phases.All these reaction layers grew in a parabolic manner as a function of bonding temperature.Rodlike B2 phase has the lowest growth activation energy of 125.2 kJ/mol,and the growth activation energy ofτ3-Al3Ni Ti2+TiAl layer near B2 phase is much lower than that near FCC phase.The penetration phenomenon and convex structure formed in the diffusion zone,which resulted in interlocking effect and enhanced the strength of resultant joints.The highest shear strength of 449 MPa was achieved at 950℃.And the brittle fracture generally initiated at the interface between Al(Co,Ni)2Ti andτ3-Al3NiTi2+TiAl layers.

Performance of GH4169 brazed joint using a new designed nickel-based filler metal via cluster-plus-glue-atom model

A novel Ni-Cr-Si-B filler metal with the cluster formula of[Cr-Ni12]B2Cr+[B-Ni8Cr]BSi Cr based on the cluster-plus-glue-atom model was designed for vacuum brazing GH4169 alloy.The effect of brazing temperature and brazing time on microstructure and shear strength of GH4169 alloy joints was investigated.The brazed seam was mainly composed ofγ-Ni solid solution.(Nb,Ti)-rich phase and(Cr,Nb,Mo)-rich borides distributed in diffusion zones.The diffusion and aggregation of B,Cr,Nb,and Mo resulted in the variation of phase contrast and morphology of borides.Coarse precipitations in the joint brazed at1240℃consisted of borides,Laves phase andδphase.The shear strength of joints was principally dominated by the brittle precipitations in diffusion zone,and the homogenization of microstructure improved the room-temperature shear strength to 820 MPa with the high-temperature shear strength of 627 MPa for the joint brazed at 1240℃/20 min.The joint fractured in diffusion zone and brazed seam,and the existence of borides and Laves phase in diffusion zone provide the potential origin for crack growth.

Carbide precipitates and mechanical properties of medium Mn steel joint with metal inert gas welding

Medium Mn steel was metal inert gas(MIG)welded with NiCrMo-3 and 307 Si filler wires.The effect of filler wires on the microstructure and mechanical properties of joint was investigated,and the carbide precipitates were contrastively discussed.The results revealed that the microstructure of weld metal,heat-affected zone and base metal are austenite.Obvious grain coarsening occurred in the heat-affected zone(HAZ),and the maximum grain size grew up to 160μm.In HAZ,C and Cr segregated at grain boundaries,the carbides was identified as Cr7 C3.The dispersive(Nb,Mo)C phase was also found in weld metal with NiCrMo-3 filler wire.All the welded joints failed in HAZ during tensile tests.The tensile strength of welded joint with NiCrMo-3 filler wire was 675 MPa,which is much higher than that with307 Si filler wire.In comparison to base metal,higher microhardness and lower impact toughness were obtained in HAZ for these two welded joints,which was attributed to the precipitation of Cr7 C3 phase and grain coarsening.The impact toughness around the fusion line is the worst for these two welded joints.

Design and experiment of the components for soil flow direction control of hilling machine based on EDEM

Cultivation and hilling are important steps in crop field management and provide an important guarantee of crop quality and quantity.With the aim of addressing how the soil flow direction of a traditional cultivation and hilling machine is difficult to control,and because it is difficult to achieve high ridge soil cultivation,among other issues,the components of the soil flow direction control of a hilling machine was designed.The components of the soil flow direction control consisted of a soil-feeding plough device,spiral knives and guide cover devices,etc.The design and analysis of the guiding parts for the two tools of the soil-feeding plough device and the spiral knife were performed to obtain an appropriate guide wall and helix angle.The guiding principle in the flow direction control components was analyzed.The design of the guide wall adopts the torsional columnar plough surface,and the elementary line angle changes from stable to increasing.The analysis of spiral milling showed that when the spiral angle is large,the milling effect is better.According to the discrete element method,the working part of the machine-soil interaction model was established.EDEM software was used to simulate the control components for the soil flow direction of the hilling machine for compound cutting.The design method with a two-factor comprehensive test was used to study the linear velocity along the outer part of the spiral knife and the influence of the forward velocity of machine of the implement on the soil cultivation effect.The results of the discrete element simulation showed that both the linear velocity along the outer part of the spiral knife and the forward velocity of the machine have extremely significant effects on the transportation of particles to the ridge top and the hilling thickness.Following multiple comparisons of the average hilling thickness with different linear velocities along with the outer spiral knife and different forward velocities of the machine,it is concluded that the performance of the machine is better when the linear velocity along the outer spiral knife is 3.01 m/s and the forward velocity of the machine is 0.7 m/s.The research conclusion had great theoretical value and practical significance for the design of the machine,which worked for cultivation and hilling.