Study On Hot Deformation Behavior And Recrystallization Behavior Evolution Of Hot Pressing Sintered NiAl

With the prosperous development of aerospace industry,there is an urgent demand for ultrahigh sound speed of aircrafts.Searching for lightweight candidate alloys with excellent properties while serving in high temperature is the key to tackle the speed bottleneck.The NiAl intermetallic,the material with propitious high temperature properties and low density,is widely considered as one of the most promising high temperature structural materials.Nevertheless,inferior room temperature ductility is the obstacle hindering large-scale application.The thermomechancial processing is one of the effective way to achieve synergistic improvement of both room temperature strength and ductility.The deformation parameters,however,are closely associated with microstructures,i.e.properties.Therefore,it is of great significance to estab lish the relationship between deformation parameters and microstructures.Besides,deformation-induced texture will have a remarkable effect on the deformability of components.Hence,taking the texture into consideration is essential for obtaining components with a desirable microstructure.Ni and Al element powders are used as starting materials.Based on Al-Ni binary phase diagram,favorable sintering technology is determined.Hot pressing sintering is employed to fabricate bulk NiAl alloys.The hot compression tests are conducted on a Gleeble-1500 D simulator in the temperature range of 1100¹300? and strain rate range of 10-3¹s-1.By analyzing the mechanical response in the uniaxial compression tests,the hot deformation behavior of NiAl alloys is determined and Arrhenius-type constitutive equation is established.Zenner-Hollomon parameters are used to evidence the validity of the as-established equation.In addition,in situ tensile testes are conducted to further understand the hot deformation behavior of NiAl alloys.The results reveal the mechanical response when varying strain rate and the reason that NiAl alloys have a superior high temperature ductility.Based on the deformation behavior,hot processing maps are stabled according to dynamic material model,through which the ideal hot processing window is determined.Hot forging is performed according to ideal hot processing window.After forging,the elongation of NiAl alloys increases pronouncedly.In addition,the fracture mode analysis shows that in the tensile tests at a strain rate of 10-3s-1 and high temperature,brittle intergranular fracture changes to ductile fracture after forging.While in the tensile tests at a strain rate of 10^-2s^-1 and high temperature,hot forging results in variation of brittle cleavage fracture to ductile fracture after forging.In the room temperature tensile tests,comparison of fracture surface of original and forged NiAl alloy reveals that brittle transgranular fracture transits into mixture mode of brittle cleavage fracture and ductile fracture.Microstructure evolution is characterized via analyzing grain boundary morphology,grain orientation gradient and GOS value.The result shows hot deformation at a high strain rate and moderate deformation temperature,softening process is consisted of continuous dynamic recrystallization and discontinuous dynamic recrystallization,while discontinuous dynami c recrystallization occurs in the deformation condition of high deformation temperature and moderate strain rate.Besides,it is found that for hot deformation of NiAl alloy,continuous dynamic recrystallization give rise to enhancement in texture intensity while discontinuous dynamic recrystallization decreases texture intensity.The former can be explained by progressive subgrain rotation and replacement of DRX grains to original deformed grains is responsible to the later.The sintered products has a weak texture component {111}<uvw>.After hot compression deformation at 1100 ?/10^-2s^-1,texture components are consisted of {110}<111> and {112}<111>.