Characteristics and Formation Mechanism of Near α Type High Temperature Titanium Alloy Combustion Microstructure Under Oxygen Enriched Conditions

Abstract:

TA19 titanium alloy was ignited by friction oxygen concentration method, and two ignition damage samples after critical ignition and sustained combustion under oxygen enriched conditions were obtained. The phase composition, microstructure morphology and its formation mechanism of TA19 titanium alloy combustion products were studied by scanning electron microscopy (SEM), energy spectrum analysis (EDS) and X-ray diffraction (XRD). Results show that: The critical ignition products of TA19 titanium alloy mainly include TiO, Ti3O, rutile type and anatase type TiO2, and the initial combustion temperature is about 500℃. While the sustained combustion products of TA19 titanium alloy mainly include TiO, rutile type TiO2. Combined with the tetragonal structure ZrO2 formed in the fusion zone, the continuous combustion temperature is judged to be above 1170℃.Four distinct zones form from the combustion surface to the alloy matrix, and they are in the sequence of combustion zone, fusion zone, heat-affected zone and transition zone. During critical ignition, Zr solid solution rich in O, α-Ti solid solution rich in O and β phase rich in Al/Sn/Mo are formed in the fusione zone; A large amount of α-Ti solid solution rich in O and a small amount of β phase rich in Al/Sn/Mo are formed in the heat-affected zone. During sustained combustion, Al solid solution rich in O, Zr solid solution rich in O, α-Ti solid solution rich in O and β phase rich in Al/Sn/Mo are formed in the fusion zone; A large amount of α-Ti solid solution rich in O and a small amount of β phase rich in O and Zr are formed in the heat affected zone, finally they form a dense layered structure that prevents the inward diffusion of O and outward diffusion of Ti. In the combustion process of TA19 titanium alloy, the element Zr first diffuses into the interface of the fusion zone, followed by Al. This is different from that Al first diffuses to the interface of the fusion zone during the combustion of TA15 titanium alloy. The reason may be that the Zr content in TA19 titanium alloy is twice that in TA15 titanium alloy, and the activity of Zr is higher. The main combustion mechanism of near α type titanium alloy is the formation of O- rich solid solution. From the perspective of microstructure, higher equiaxed phase content is conducive to the dissolution of oxygen; From the point of view of alloy composition, proper control of the content of Ti, Al and Zr is beneficial to obtain dense O-rich solid solution.

Key words:near α type titanium alloy; burning microstructure; alloying elements; combustion mechanism