Effect of two-step solid solution on microstructure andδphase precipitation of Inconel 718 alloy

Inconel 718 is the most popular nickel-based superalloy and is extensively used in aerospace,automotive,and energy indus-tries owing to its extraordinary thermomechanical properties.The effects of different two-step solid solution treatments on microstructure andδphase precipitation of Inconel 718 alloy were studied,and the transformation mechanism fromγ″metastable phase toδphase was clarified.The precipitates were statistically analyzed by X-ray diffractometry.The results show that theδphase content firstly increased,and then decreased with the temperature of the second-step solid solution.The changes in microstructure andδphase were studied by scanning electron microscopy and transmission electron microscopy.An intragranularδphase formed in Inconel 718 alloy at the second-[100]_(δ)[011]γ step solid solution temperature of 925℃,and its orientation relationship withγmatrix was determined as//and(010)_(δ)//(111)γ.Furthermore,the Vickers hardness of different heat treatment samples was measured,and the sample treated by second-step solid solution at 1010℃ reached the maximum hardness of HV 446.84.

Phase and CCT Diagram of an N-Containing 8%Cr Roller Steel

The pseudo-equilibrium phase diagram and continuous cooling transformation diagram of an N-containing 8％ Cr roller steel were investigated by using thermodynamic calculation,differential scanning calorimetry,Ⅹ-ray diffraction,expansion method,and so on.Under equilibrium conditions,the main carbonitrides are MX,M7C3,and M23C6 types.The measured Ac1,Ac3,start temperature of martensitic transformation,and M7C3 transformation temperatures are 811,855,324,and 1100 ℃,respectively.Bainite appears at cooling rates ranging from 0.5 to 5 ℃/s and ferrite forms at grain boundaries at a cooling rate lower than 0.5 ℃/s.Finally,the effects of adding N and lowering the C content on workability and mechanical properties of common 8％Cr steel were discussed.

Preparation of ultrafine α-Al_2O_3 powders by catalytic sintering of ammonium aluminum carbonate hydroxide at low temperature

The precursor of ammonium aluminum carbonate hydroxide was synthesized by using aluminum sulfate（Al2（SO4）3） and ammonium carbonate（（NH4）2CO3）. The effects of α-Al2O3 seeds and mixture composed of α-Al2O3 and ammonium nitrate, as well as multiplex catalysts （AT） on phase transformation of alumina in sintering process were investigated respectively. The results show that the α-Al2O3 seeds and the mixture of α-Al2O3 and ammonium nitrate can lower the phase transformation temperature of α-Al2O3 to different extents while the particles obtained agglomerate heavily. AT has great potential synergistic effects on the phase transformation of alumina and reduces the phase transformation temperature of α-Al2O3 and the trends of necking-formation between particles. Therefore the dispersion of powder particles is improved significantly.