Hydrogen Embrittlement For The Welded Joint Of TA16 Alloy And TA19 Alloy

TA16 and TA19 alloy have been developed as new Ti alloys in recent years in China, the alloys are welded to manufacture a key facility in some important engineering. The welded joints are the weaken parts when applied in high-temperature and high-pressure environment due to the welding stress, welding defects, temperature gradient and the structural transformation, so it is necessary to study the hydrogen embrittlement of TA16 and TA19 alloy welded joint, and it is also the first study in China.The morphologies, distributions and type of hydrides in welded joint were studied by OM, SEM and TEM. The mechanic properties (E, S) of hydride are analyzed by Nano indenter II. The welded alloys charged hydrogen tensile tested at the rate of 4×10-6/s, 8×10-4/s and 4×10-1/s respectively, the tensile properties were tested to study the hydrogen embrittlement type, deformation characteristic and crack mechanism. The effects of hydride on crack fracture were studied by the in situ SEM. The results showed that:1. The hydrides in TA16 alloy welded joints distribute in one grain or across several grains, the morphologies are short and thin pieces like bars, short and thin or long and thin pieces like needles. The hydride in TA19 alloy welded joints distribute inside one grain or along grain boundaries, the morphologies are short and thin pieces like needles, short and wide pieces ,and small and round pieces, and the II-type hydrides are founded.2. The long and thin hydride pieces are 8-TiH, the short and wide hydride pieces are r-TiH, and the small and round hydride pieces are also 8-TiH.3. The H content from 0.037% to 0.099% has little effect on the σb and σ0.2 of TA16 alloy, while the δ5 deduced greatly, and the HE occurred under the stain rate of 4× 10-6/s, when under the stain rate of 8 × 10-4/s to 4 × 10-1/s, σb and σ0.2 increase, while δ5 does not decrease. When the H content less than 0.057%, it has little effect on the σb and σ0.2 of TA19 alloy welded joint, while the δ5 deduced greatly under the stain rate of 4× 10-6/s to 4× 10-1/s, when the H content more than 0.057%, the properties of welded joint decreased sharply and the embrittlement occurred.4. TA16 alloy matrix metals submit to dimple rupture mechanism, the hydrogen content of 0.037% to 0.099% and the strain rate of 4× 10-6/s to 4× 10-1/s have little change to themechanism. The rupture of TA19 alloy welded joints change from transgranular fracture mechanism to a mixed fracture mechanism of intercrystalline frature and hydride-cleavage fracture with hydrogen increasing from 0.025% to 0.11%, grain boundaries and the lath a structure interfaces are the cracked planes.5. Hydride pieces are fracture sources in TA16 alloy, which offered the paths of cracks expansion. Hydrides weaken the grain boundaries of TA19 alloy welded joints, which accelerate the collapse of grain boundaries and decrease strength and elongation.