Preparation And Investigation Of Property For FeCrAl Alloy By Hot Isostatic Pressing

Fe-Cr-Al alloy has good corrosion resistance and high temperature oxidation resistance.It is widely used in the industry to prepare heating elements and high temperature structural parts.Comparing with the Fe-Cr-Al alloy prepared by ordinary metallurgy methods,the Fe-Cr-Al alloy prepared by powder metallurgy has better performance.By adding elements,such as Mo and Y,and introducing stable nano-oxidized particles,the mechanical properties of the alloy can be effectively improved.In this thesis,the influence mechanism of impact toughness and tensile properties for the prior particles boundary of Fe-Cr-Al alloy,prepared by powder metallurgy,had been investigated.And the effects of Al,Mo and Y content on the microstructure and tensile properties of Fe-Cr-Al alloy were analyzed.The influence of pre-oxidation treatment temperature of Fe-Cr-Al-Y alloy prepared by STARS method on the microstructure and tensile properties were explored.The main results are listed as follows:(1)Precipitations at the boundary of the prior particle boundaries distributed at the grain boundaries of the Fe-Cr-Al alloy are mainly carbonitrides of Nb and nitrides and oxides of Al.During the deformation process,microcracks are initiation and propagation at the precipitation phase of the prior particle boundaries.And the alloy had poor toughness.The large-size Al₂O₃ precipitations continuously or dispersely distributed along the grain boundaries lead to lower tensile strength and poor plastic deformation ability of Fe-Cr-Al alloy at room temperature and 500?.The alloy occures intergranular fracture at room temperature.With rolling and subsequent heat treatment,the continuous large-sized grain boundary precipitates in the Fe-Cr-Al alloy are significantly fragmented,and it is effective way to eliminate the adverse effect of prior particle boundaries precipitations on the alloy performance.Part of Al₂O₃ and Ti O₂ precipitations reacted with Y and Y₂O₃precipitations to form more stable Y-Al/Ti-O phases.(2)There was no obvious segregation of components occurred on the surface and inside of gas atomization powders of the Fe-22Cr-2Al-0.4Y,Fe-22Cr-3Al-3Mo and Fe-22Cr-2Al-5Mo alloy.In the process of hot isostatic pressing,the oxygen in the oxides of Fe and Cr on the surface of the Fe-22Cr-2Al-0.4Y alloy powders reacts with the Y element in the matrix to precipitate oxide particles of Y at the grain boundaries.The precipitations present in Fe-22Cr-3Al-3Mo and Fe-22Cr-2Al-5Mo alloys are mainly fine Al-rich nitrogen and oxides distributed in the grain boundaries and within the grains,and large-size Cr-rich carbide or carbon oxide distributed along the grain boundaries.The tensile strength of Fe-22Cr-2Al-0.4Y alloy are 797 MPa and 535 MPa at room temperature and 500?,and the elongation are of 9%and 24%,respectively.The tensile strength of Fe-22Cr-3Al-3Mo alloy at room temperature and 500? are 787MPa and 524MPa,and the elongation is 18%and 26%,respectively.With decreasing content of Al and increasing content of Mo,the tensile strength of Fe-22Cr-2Al-5Mo alloy at room temperature and 500?are 717 MPa and 572 MPa,elongation are 4%and 27%.There are more large-sized Cr carbides and carbon oxide at the grain boundaries is the main reason for Fe-22Cr-2Al-5Mo alloy had brittle fracture at room temperature.(3)When preparing Fe-Cr-Al-Y alloy powder by STARS method,the oxidation treatment temperature should be about 400?.When the oxidation treatment temperature is higher than 800?,the powder surface is covered with a stable Al₂O₃scales and result in an ineffective metallurgical bond between the powder particles in the subsequent hot isostatic pressing process,and the strength of alloy is reduced.When the oxidation temperature is lower than 600?,with the increase of the oxidation temperature,the density of nano-precipitated phases distributed at the grain boundaries of the alloy increases,and the strength of the alloy firstly increases and then decreases.The densely distributed precipitates at the grain boundaries will increase the strength and reduce the plasticity of alloys.