基于相变调控的Ti551钛合金热处理工艺优化OA

The effects of heat treatment parameters including solution temperature,aging temperature and cooling rate on the microstructure and mechanical properties of a new medium-strength and high-toughness Ti551 alloy were investigated by means of optical microscopy,scanning electron microscopy and universal tensile testing machine.With the same solid solution temperature at 900℃,no obvious changes were observed in the content and size of primary α phase of alloy,while the lamellar thickness of secondary α phase increased from 0.26 μm to 0.42 μm with the aging temperature increasing from 550℃to 650℃.With the same aging temperature of 550℃,the content of the primary α phase de-creased from 45%to 15%as the solution temperature increased from 900℃to 950℃,along with con-tinuous refinement of grains and morphological transformation from short rod-like to equiaxed.The lamellar thickness of the secondary α phase increased accordingly,reaching up to 0.72 μm after alloy subject to solid solution treatment at 950℃.The morphological feature and size of the microstructure are decisively influenced by the cooling rate:an almost single fully equiaxed primary α phase micro-structure is obtained by furnace cooling,whereas the primary α phase is refined and the precipitation of coarse lamellar secondary α phase is promoted by moderate cooling.The results show that optimal strength-toughness combination of the Ti551 alloy is achieved under the composite heat treatment of 900℃×2 h+air cooling,then followed by 550℃×6 h aging,which is closely associated with the regu-latory role of cooling rate.Acicular secondary α phase can be induced in the transformed β microstruc-ture by higher cooling rate,and the alloy's strength-plasticity matching effect is further enhanced by the subsequent aging treatment.