Top Publication Acta Materialia In-Situ Customized Microstructure and Properties during Additive Manufacturing of Ti6Al4V _ Parameters

Original Title Top Issue Acta Materialia In-situ Customization of Microstructure and Properties in Additive Manufacturing of Ti6Al4V At present additive manufacturing technology which is developing in full swing in the research ti6al4v field and engineering application market is a revolutionary technology that can produce metal parts with reliable performance Moreover the products manufactured by adding materials can either be applied directly without post-processing or can be put into use only after uncomplicated post-processing However the problem of Ti6Al4V alloy products manufactured by powder-spreading laser additive manufacturing is that the strength is excessive and the toughness is insufficient This is because the needle-like α 'martensite is inevitably formed in the region where the columnar crystal β phase is preferentially grown in the structure In engineering practice in order to eliminate the adverse effects of α ' it is necessary to carry out heat treatment In order to overcome this shortcoming a novel SLM process was developed to transform the unwanted α 'martensite into a lamellar α + β structure by in-situ decomposition and to control it within a tunable range of size The alpha + beta structure of this sheet results in mechanical property data for printed ti6al4v articles that exceed the property data specified in ASTM And exceeds the performance of Ti6Al4V alloy products obtained by other additive titanium round bar manufacturing technologies Moreover we also found that the lattice parameters of the β phase can be used to predict whether the in-situ decomposition of α 'martensite occurs in SLM Ti6Al4V alloy This study can be said to be a very important step in how to customize the microstructure of Ti6Al4V alloy by SLM technology This work was published in Acta Materialia the top journal of materials Screenshot of the original source of the paper Microstructure is as relevant to the macroscopic properties of most materials as a person's fingerprint For the traditional metal casting process it is the most common means to achieve the desired mechanical property by controlling the microstructure through appropriate process control For powder-spread 3D printing it is not easy to precisely control its microstructure This is because the interaction between the high energy beam and the powder is a very intense and very fast dynamic process Moreover the thermal history process in the process of powder spreading and additive manufacturing is quite complex This brings a great challenge for SLM technology to obtain high performance Ti6Al4V alloy Ti6Al4V is the most widely used alloy in titanium industry which is called the old cattle in titanium industry Generally speaking the strength of Ti6Al4V alloy made by SLM additive is generally better than that of deformed parts with the same composition but its plasticity and toughness are relatively insufficient for engineering applications It needs to be improved by subsequent heat treatment The reason for the lack of plasticity and toughness is that α 'martensite which we do not expect grows in the β crystal where the columnar crystal grows preferentially and α' martensite is easy to become the source of crack titanium sheet grade 5 initiation and propagation Resulting in the need for heat treatment to improve the situation The post-processing operation makes the SLM technique less effective Sketch of research results of the paper Expand the full text The biggest challenge to solve this problem is how to replace α 'martensite with the desired α + β phase under controlled conditions What is more important is how to transform α 'martensite into a series of lamellar α + β phases in the adjustable scale range Thereby achieving different combinations of strength and toughness to minimize or avoid post-processing Recently we proposed a method to transform acicular α 'martensite into α + β phase in situ by properly changing the process parameters of SLM (such as focus deviation distance FOD) and energy density E) In this case the thickness of the alpha phase lath is in the range of 02 to 03 microns This ultrafine microstructure also results in the as-deposited material having an ultrahigh yield strength (the yield strength can reach 1106 ± 6 MPa and the elongation 114 ± 04%) ti6al4v eli

However because the adjustable range of the distance of FOD is too narrow the range of process parameters that can be changed is too narrow and titanium alloys are quite sensitive to the parameter of FOD resulting in little practicality If not heat treated It basically has no practical value The current goal is to achieve a wide parameter tuning range of the as-deposited microstructure of Ti6Al4V alloy Microstructures of Ti6Al4V alloys produced by two different techniques SLM and EBM (A) the temperature of the manufacturing platform is 200 deg C the layer thickness of each layer is 30 microns during titanium plate gr7 manufacturing and alpha 'martensite is obtained; (B) the layer thickness of each layer is 50 microns during manufacturing and alpha + beta lamellar structure is obtained when the preheating temperature of the manufacturing platform is 730 deg C This study is based on the assumption that the growth characteristics of successive layers in additive manufacturing can be used to control the thermal properties of the previous solidified layer Under normal SLM manufacturing conditions α 'martensite is the predominant phase formed However by properly setting the process parameters we assume that the temperature of each pre-solidified layer can be raised in situ As a characteristic of SLM additive manufacturing the temperature of each layer can be very high such as reaching a controllable range (600 ~ 850 ℃) which can effectively promote the decomposition of α 'martensite If we can maintain this set temperature for a long time α 'martensite can be completely decomposed Moreover if the expected temperature rise is maintained (600-850degree C) the anisotropy of the material will be promoted and the residual stress of the material will be reduced Microstructure obtained during custom fabrication of SLM at different parameters with a fabrication diameter of 12 mm Therefore this article reports our latest research results We found that through the design of innovative SLM process route the plate-like α + β phase can be generated in situ from α 'martensite and it can be controlled within the adjustable range The range is 015 to 08 microns Another significant advantage is that the innovative system allows the transformation of columnar crystals to equiaxed beta phases As a result a Ti6AL4V alloy with excellent combination of strength (yield strength 1020 to 1110 MPa) and toughness (11 to 15%) is realized by SLM Furthermore the in situ α 'martensite decomposition also results in a decrease (reduction) in residual stress Different microstructures obtained by SLM customization when the sample size is changed Microstructure of different areas at different magnification Source of paper WXu;EWLui;APateras;MQian; MBrandt; In situ tailoring microstructure in additively manufactured Ti-6Al-4V for superior mechanical performance[J] Acta MaterialiaVolume 125 15 February 2017 Pages 390-400 Https//doiorg/101016/jactamat201612027 back to Sohu to see more Responsible Editor