The impact of hot isostatic pressing temperature on the crack propagation rate of selective laser melted TA15 alloy
Selective laser melting(SLM)technology has attracted much attention from the aeronautics and astro-nautics realm due to its advantage of high degree of freedom,high accuracy,and good mechanical properties after printing.Considering the durability and designing concept of damage tolerance of structural materials,the crack propagation rate of components applied into aeronautics is regarded as one of the key points to ensure the service safety of equipment.The research of ameliorating the crack resistance of titanium alloys through post-treatment is believed to provide valuable data guidance to the further application of SLM-printed titanium-based components in the aeronautics.In the current paper,the hot isostatic pressing(HIP)process is conducted to SLM-printed TA15 alloys as the post-treatment.Specifically,the influence of the HIP temperature on the micro-structure,hardness,and crack propagation rate are investigated in details.The microstructure of the as-printed TA15 alloy HIP treated at the temperature range of 900-980 ℃ is generally identified as multi-hierarchical nee-dle or lath-like α phase.Besides,the size of the α phase gradually coarsens along with the rise of the HIP tem-perature.The average length of primary α phase ranges from 60 μm to 66 μm.Whereas,the width of primary αphase significantly increases from 2.35 μm to 5.62 μm.The hardness of the HIPed specimen resultantly reduces from 35.8 to 31.9(HRC).When the HIP temperature surpasses the phase transformation point of α to β phase,the formation of Widmannstatten structure is observed in the specimen with hardness of 32.2(HRC).The crack propagation rate of the specimens HIP treated utilizing different parameters converges and is seldomly affect-ed by the microstructure when the stress intensity factor range(△K)is within 20-50 MPa·m1/2.While the crack propagation rate gradually decreases with the rise of HIP temperature when △ K＜20 MPa·m1/2.Coarsening of multi-hierarchical needle(lath)-like α phase enhances the deflection of crack propagation path caused by micro-structure,which correspondingly retards the further propagation of cracks.Widmannstatten structure formed in the specimen HIP treated at 1 020 ℃ possesses the lowest crack propagation rate among different microstruc-tures.In addition,the packets of α phase with various crystallographic orientation inside the β phase favors the conversion of fatigue cracks propagation path,which effectively lengthens the propagation path and reduces the crack propagation rate.In summary,the coarsened multi-hierarchical lath-like α phase in the specimen HIP treat-ed at 980 ℃ and the Widmannstatten structure formed after HIP treatment at 1 020 ℃ benefit to the reduction of crack propagation rate.While the hardness of specimens suffers a certain loss.
hot isostatic pressingselective laser meltingmicrostructurerockwell hardnesscrack propagation rate
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