Deformation And Damage Behavior Of Pre-twinned Commercial Pure Titanium Under Impact Loading

Titanium has the advantages of high specific strength,fracture toughness and ease of manufacturing.Since the realization of industrial production in the 1950 s,its application field are broadened and widely used in the fields of aerospace,rail transportation,automobile manufacturing and petrochemical engineering,showing broad prospects for development.As an important material for industrial applications,titanium is often used in some extreme environments.Due to the poor symmetry of the crystal structure,deformation twinning is an important plastic deformation mode for the commercial pure titanium.Therefore,it is of great engineering significance to investigate the effect of pre-twins on the deformation and damage behaviors of pure titanium under extreme conditions.In this paper,deformation twins are prefabricated in commercial pure titanium by quasi-static compression,and different contents of twins are achieved by controlling compression strain.A single-stage gas gun is utilized to perform the spallation experiment on the pre-twinned commercial pure titanium,the free surface particle velocity history is obtained,and the spallation strength is derived.The postmortem samples are collected for microstructure characterization.The damage morphology of the postmortem samples is analyzed with optical microscope and scanning electron microscope,and the number and nucleation position of voids are counted.Deformation twins in pure titanium are characterized by electron backscatter diffraction.Under impact loading,the spallation strength of the as-received pure titanium increases with the increase of the impact velocity,and the degree of damage inside the sample shows an increasing trend.At the same impact velocity,the spallation strength of the pre-twinned pure titanium is improved compared with the as-received pure titanium,and the spallation strength increases with the increase of pre-twins content,and the degree of damage decreases.Damage in pre-twinned pure titanium mainly nucleate at twin boundaries and general grain boundaries,accompanied by a small number of intracrystalline voids.Under continuous tension,the voids grow further and form a large crack,some of them annihilate the entire twin or break the grains.The pre-twins act as additional energy release points for pure titanium under impact loading,and hinder the occurrence of spallation,thus improving its spalling strength.