Study On The Oxidation Mechanism Of Ti-Al Compound Alloys With The Valence Electron Structure Parameters

Titanium aluminum compound alloys have been developed into a kind of promising new type of high temperature alloy materials because of their excellent properties such low density,high toughness,high strength,good creep resistance and corrosion resistance,etc.However,the oxidation behavior of titanium aluminum compounds is still the bottleneck of restricted development of this alloy.Therefore,it is of great theoretical significance to study the oxidation mechanism of titanium aluminum compound alloys.By using the empirical electron theory of solids and molecules?EET?,the valence electron structures of phases and phase interfaces in titanium aluminum compound alloys are calculated;the relationship between the valence electron structure parameters and the oxidation mechanism of titanium aluminum compound alloys is established;and the theoretical analysis model of the oxidation mechanism of titanium aluminum compound alloys is also proposed.The researched results are as follows.?1?The valence electron structure parameters of basic phases?e.g.,?-TiAl,Ti₃Al,TiO₂and Al₂O₃?are calculated.The results show that the values of the bond energy of these basic phases are larger,accounting for the excellent thermostability and melting point.?2?The valence electron structure parameters of the?-TiAl cell containing oxygen atoms are calculated,and the relationship between the valence electron structure parameters and the oxidation mechanism of?-TiAl alloys is established.When the cells containing oxygen atoms are not uniformly distributed in the matrix of titanium aluminum compound alloys,the anisotropy of the crystal is enhanced,resulting in the disintegration of covalent bonds and the collapse of Ti atom.As a result,the collapsed atoms form the body centered cubic structure containing Ti atoms.And then the neighboring oxygen atoms enter the eight-hedral gaps of the body structure,and TiO₂ oxide film is formed.Meanwhile,the more atom vacancies are generated after the collapse of Ti atoms;the Al atoms diffused in vicinity can occupy these vacancies,resulting in the formation of the six square crystal type with Al atoms.Then the neighboring oxygen atoms can enter the gaps of the six square crystal type,and the stable Al₂O₃ oxide film is formed.?3?The valence electron structure parameters of the Ti₃Al cell containing oxygen atoms are calculated,and the relationship between the valence electron structure parameters and the oxidation mechanism of Ti₃Al alloys is established.When the more oxygen atoms enter the cells,the covalent bonds can be disintegrated due to the lower stability of cells.The decomposed Ti atoms can be collapsed and result in the formation of the body centered cubic structure containing Ti atoms.Meanwhile,the neighboring oxygen atoms enter the eight-hedral gaps of the body structure,and TiO₂ oxide film is formed.The Al atoms diffused in vicinity can occupy the vacancies formed by Ti atom collapse,and the six square crystal type with Al atoms is formed.Then the neighboring oxygen atoms can enter the gaps,and the Al₂O₃ oxide film is formed.?4?The valence electron structure parameters of the phase interfaces?TiAl//TiO₂,TiAl//Al₂O₃,Ti₃Al//Ti O₂,Ti₃Al//Al₂O₃?in Ti-Al compound alloys are calculated,the relationship between the valence electron structure parameters and the stability of phase interfaces.The results show that the?-TiAl?100?//TiO₂?100?interface has the smaller interface covalent bond energy difference,exhibiting the better interface binding;the Ti₃Al?0001?//TiO₂?100?interface also has good interface stability because of the smaller interface covalent bond energy difference.But the Ti₃Al?0001?//Al₂O₃?0001?interface has the larger interface covalent bond energy difference,accounting for the poor interface stability between the oxide film and matrix.