Study On Plastic Deformation Mechanism And Constitutive Relation Of Titanium Alloy

Titanium alloys are widely used in aerospace, shipbuilding, chemical, ordnanceindustries and bio-medicine fields due to their excellent mechanical properties and goodbiocompatibility. The development, application, classification and microstructure oftitanium alloys are briefly introduced in the text. And the research status of hot deformationand constitutive relation, plastic deformation mechanism and crystal plasticity model fortitanium alloys are summarized in detail. Based on the review, the specific works are givenas follows:The compression behavior of TC18alloy at elevated temperatures is described, basedon this, the hot deformation behavior of TC18alloy is analysed. The mechanical propertiesof TC18alloy during hot compression are characterized by establishing an improvedArrihenius constitutive model, and the fracture mechanism of TC18alloy under nomalcompression is analysed. And based on the Hart’s model, a microscopic constitutiverelationship is deduced which can link the physical mechanisms to the macroscopicexperimental results. By analyzing microstructure of TC18alloy after compressiondeformation at various temperatures and various strain rates, it is found that the number ofprimary alpha phase decreases and equiaxial degree of grains increases with increasingtemperature. The secondary lamellar alpha phase dispersive distributing in beta phase attemperatures range from25℃to600℃are spherized into small alpha grains at800℃.The number of alpha grains decreases with decreasing strain rates. The elongated alphagrains dominate at higher strain rates, while the number of equiaxial alpha grains is moreand the elongated alpha grains are widen at lower strain rates. Its show that alpha grainswill be a certain coarsing affected by the compression rates, widening and growth of alphagrains are advantageous under the lower compression rates.A modified Inoue Katsuro constitutive model is established by analyzing the flowstress of Ti600alloy during hot compression. The fracture mode of Ti600alloy at roomtemperature after the quasi-static compression is analyzed using scanning electronmicroscopy (SEM) and results show that the alloy is mainly of brittle fracture with someductile fracture in the local region of the fracture surface.Based on Arrhenius constitutive model, the stress constitutive model of Ti40alloywhich suits wide temperature range is proposed and parameter values for the model are determined by analyzing experimental data. And then the precision of the model is analyzedqualitatively and quantitatively, the reliability of the model was verified. By analyzingmicrostructure of Ti40alloy after compression deformation at various conditions, it isfound that beta grains in the center of Ti40alloy is smashed seriously at higher strain rates,and grains is not cracked significantly when strain rates are reduced. The reason is thatadiabatic thermal rising of Ti40alloy drops greatly with decreasing strain rates. The shapeof beta grains changes and grain boundaries become blurred gradually with increasingtemperatures, the ability of the alloy to resist deformation is reduced. The reason is that betagrain boundaries and part of beta grains are “liquefied” so that recrystallization occurs withincreasing temperatures.Based on discussion in the evolution of slip and twinning of the two plasticdeformation mechanisms, by adopting Bassani and Wu’ hardening model, and using theplastic velocity gradient to denote plastic deformation of the single crystal, the constitutiverelationship of the single crystal in the meso-scale is founded. And by introducing theconcept of equivalent inclusion to determine the relation between mesoscopic physicsquantities and macroscopic physics quantities, an elastic-viscoplastic self-consistent modelfor HCP polycrystalline materials is established.