Microstructure And Mechanical Properties Of Ni₃Al-based Alloy Processed By Laser Metal Deposition

Ni₃Al intermetallic compound has special long-range ordered crystal structure,strong atomic bonding,high deformation hardening rate,special yield strength and temperature abnormal effect,thus it has broad application prospects in aerospace and other fields.The traditional Ni₃Al alloy forming process is relatively mature.This article explores a new forming process of Ni₃Al alloy,laser metal deposition.In this paper,through single-pass deposition experiments,the effect of laser forming process parameters on the height,width and surface quality of the deposited layer was studied.Through thin-wall deposition experiments,the influence of the forming environment and laser forming process parameters on the geometry of the deposition layer and the tendency of thermal cracking was studied.From these experiments,a reasonable range of laser forming process parameters for direct laser deposition of Ni₃Al alloy was determined.A laser forming process with a laser power of 1200 W,a scanning rate of 900mm/min,a powder feeding rate of 15 g/min,a lap rate of 40%,and an elevation rate of 0.4mm,that is,the laser line energy density is 1.33 k J/m,and the powder line mass density The16.7 g/m sample has better forming quality.Meanwhile,the laser metal deposition forming process needs to be carried out in an argon-filled environment;although the inter-pass pause can provide enough time for the deposited layer to release energy,the acceleration and deceleration process of the laser probe will cause serious shape distortion.The dendrites of the laser-deposited layer of Ni₃Al alloy are?+?'eutectic phase structure,and there are large-grain?'phase inclusions between the dendrites,and the shape of the inclusions is irregular.At the same time,through SEM and extraction XRD analysis,there are still large-size boride(M₂₃B₆)and small-size but unevenly distributed?-Ni Al phase between the dendrites.The Ni₃Al alloy laser direct deposition forming parts have good mechanical properties.The yield strength under static tension at room temperature reaches 540 MPa,the tensile strength is 1160 MPa,and the elongation after fracture is 27%.In addition,the alloy exhibits a typical yield strength-temperature anomalous effect.The yield strength of the alloy increases significantly with the increase of the tensile temperature.When the temperature exceeds 450?,the rate of increase of the yield strength of the alloy slows down,and the alloy enters the weakening temperature at 850?.The alloy has a yield strength of 640 MPa and an elongation after fracture of 11%under static tension at a high temperature of 650?.Due to the limitation of the microstructure of Ni₃Al alloy formed by direct laser deposition,the mechanical properties of the alloy have not been fully utilized.In this paper,the"Solid Solution+Aging"heat treatment method has effectively improved the structure of the alloy and further improved the mechanical properties of the alloy.Among them,the"1080?×4 h,AC+900?×10 h,AC"process solution aging treatment is an ideal heat treatment process for optimizing laser deposition of Ni₃Al alloy that can effectively avoid the precipitation of?-Ni Al high temperature hard phase,while generating fine??phase and boride dispersion strengthening microstructureIn this paper,by integrating the Ni₃Al-based alloy direct laser deposition forming process and the development trend of single-crystal Ni₃Al-based alloys,an attempt was made to prepare single-crystal Ni₃Al-based alloys by laser seeding.The feasibility of Ni₃Al-based alloy single crystal laser seeding technology was initially explored.Through microstructure analysis,the alloy has a certain directional dendrites,which proves that it is feasible to prepare single-crystal Ni₃Al-based alloys by laser seeding.