Study On The Process And Properties Of Porous Nickel-based Alloy Metal Made By Laser Additive Manufacturing

Laser additive manufacturing is the latest rapid prototyping technology.Utilizing high laser energy to melt metal powder and manufacture prototype directly layer by layer.Nickel-based alloy is metal with excellent physical,chemical and mechanical properties and widely implemented into aerospace and chemical engineering industry fields.This thesis focuses on study of porous Nickel-based prototyping made by Laser additive manufacturing technology.Deloro 40 nickel-based alloy is used as experimental material and YAG-300 W is used as manufacturing equipment to study industrial process parameter.The study can be divided into three steps based on principle of laser additive manufacturing technology: single-layer single-channel scanning,single-layer multi-channel scanning and multi-layer multi-scanning.With this analysis routing,the research explores influence principle of the laser power,the laser frequency,the laser pulse width and the scan interval.It can be achieved for successful formability of porous nickel-based alloys.Using optical microscopy and XRD analysis,etc.the microstructure and formal phases of porous nickel-based alloy are studied.With Hardness test and electronic universal testing bench analyze are to reveal relevant microstructure and macroscopic mechanical properties of porous prototypes.The result is confirmed: the width of laser scanning line is increased as laser power,pulse width and frequency growing,then stabilizing when above parameter reaching a certain value;the over large and over small parameters will be not good to obtain porous moldability of prototypes.The optimal process parameters are as following: the laser power from 110 W to 130 W,the laser pulse width from 2.0ms to 4.0ms,the laser frequency from 10 Hz to 15 Hz,and the scan interval from 0.6mm to 0.8mm.With above mentioned optimal parameter,the porous Nickel-based prototype can be manufactured with better formability.The measured porosity of prototypes is from 12% to 32% with above mentioned optimal process parameter.With laser heat-affected zone effect,semi-molten nickel based alloy powder attaches inside of holes' wall in porous nickel-based prototypes which result in actual porosity is smaller than that compared with designed.Study on Microstructure of porous prototypes explores that: Deloro 40 nickel-based alloy's microstructure is composed of dendrite grain;dendrite grains grow with layers stacked direction;also equiaxed grain exists during laser cladding.Due to the microstructure caused by laser additive manufacturing and existence of hard phase,the prototypes' micro-hardness is as high as HV570.The compressive characters of porous prototypes have relationship with porosity of prototypes.Compressing the prototypes to crack,observation shows brittle fracture characters.Focus on common defects of porous nickel-based alloys,"crack","balling" and "warpage" phenomenon,the defects formation mechanism and the methods how to reduce appearance of these defects were investigated.