A new approach to correlate the defect population with the fatigue life of selective laser melted Ti-6Al-4V alloy

The effect of defect population on the anisotropic fatigue resistance of AlSi10Mg alloy fabricated by laser powder bed fusion

Arc additive manufacturing technology has high deposition efficiencies and material utilization rates. However, the large heat input and high temperature gradient during arc additive manufacturing process lead to the formation of the coarse columnar grains. Due to the presence of the coarse columnar grains, the mechanical properties of the part have great anisotropy which limits the application of it. In this experiment, a method named hot-wire arc additive manufacturing was adopted to reduce the arc heat input and refine the columnar grains, and four thin-walled samples with the material of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si were manufactured. It is interesting to find that the coarse columnar grains have been greatly refined, and finally a part consisting of equiaxed grains and short columnar grains was obtained. At the same time, the width of the α-lath has also been refined. The mechanical properties are in accordance with the grain changes and the anisotropy almost disappeared. And it seems that a part with comprehensive mechanical properties can be obtained by the hot-wire arc additive manufacturing.

Reducing arc heat input and obtaining equiaxed grains by hot-wire method during arc additive manufacturing titanium alloy

Defect formation is a critical challenge for powder-based metal additive manufacturing (AM). Current understanding on the three important issues including formation mechanism, influence and control method of metal AM defects should be updated. In this review paper, multi-scale defects in AMed metals and alloys are identified and for the first time classified into three categories, including geometry related, surface integrity related and microstructural defects. In particular, the microstructural defects are further divided into internal cracks and pores, textured columnar grains, compositional defects and dislocation cells. The root causes of the multi-scale defects are discussed. The key factors that affect the defect formation are identified and analyzed. The detection methods and modeling of the multi-scale defects are briefly introduced. The effects of the multi-scale defects on the mechanical properties especially for tensile properties and fatigue performance of AMed metallic components are reviewed. Various control and mitigation methods for the corresponding defects, include process parameter control, post processing, alloy design and hybrid AM techniques, are summarized and discussed. From research aspect, current research gaps and future prospects from three important aspects of the multi-scale AM defects are identified and delineated. 

Multi-scale defects in powder-based additively manufactured metals and alloys

Effects of build direction on tensile and fatigue performance of selective laser melting Ti6Al4V titanium alloy

The effects of crack growth direction on the fatigue crack growth of wire arc additive manufactured Ti-6Al-4V were studied. The fatigue crack growth rate (FCGR) of horizontal and vertical samples has different stress intensity factor transition point, ΔKT, which is 11.3 MPa m1/2 and 10.3 MPa m1/2, respectively. The FCGR of vertical sample is 5% higher than that of horizontal sample when the stress intensity factor, ΔK is smaller than ΔKT. The difference in FCGR is resulted from the microstructure characterization and the fatigue crack growth direction.

Anisotropy of fatigue crack growth in wire arc additive manufactured Ti-6Al-4V

The invention proposes an added material manufacturing method under a vibration condition In an arc wire feeding added material manufacturing or laser powder feeding melting added material manufacturing process, mechanical vibration with a certain frequency is synchronously introduced, so that parts are located in a micro vibrating state; and the mechanical vibration acts on a micro liquid-state molten bath formed in the added material manufacturing process to refine grains, so that the structure becomes more uniform, and such phenomenon as air holes, inclusions and incomplete fusion is reduced or even eliminated Meanwhile, the vibration acts on metal just condensed, so that the stress generated by vibration and residual stress generated in the added material manufacturing process are superposed to generate local plastic deformation to achieve the purpose of reducing residual stress and deformation of added material manufacturing parts, and the added material manufacturing parts under vibration condition are more excellent in performances

Added material manufacturing method under vibration condition

A new recrystallization without plastic deformation was observed at the semi-coherent micro-lamella (ML) of wire arc additive manufactured Ti6Al4V, which is driven by the interface energy and the dislocation-induced elastic strain energy. It was classified into three types according to nucleation site, which are the recrystallization at the boundary of colony structures, inside the colony structures, and at the boundary of basket weave structures, respectively. Some new behaviors in the nucleation and growth of this recrystallization were found. Firstly, the nucleation mechanism of one direction strain and interface induced grain boundary migration was found in the recrystallizations at colony boundary and inside the colony. Secondly, the recrystallized grains at colony boundary grew to be part of the original colony, while the others grew to be a new grain. Relevant mechanisms were discussed according to theoretical calculation of driving energy and grain growth behaviors. Because the continuous grain boundaries were broken by this recrystallization, not only the ultimate tensile strength was increased by 100 MPa or so, but also the ductility anisotropy was decreased from the 4.8% of as-deposited sample to the 0.2%. The results would provide a new approach without plastic deformation to improve the performances of additive manufactured components.

A new recrystallization at semi-coherent micro-lamella and its effect on tensile properties of wire arc additive manufactured titanium alloy

Grain boundary discontinuity and performance improvement mechanism of wire arc additive manufactured Ti–6Al–4V

Effects of alloying elements of Si and Sn on weld characterizations of laser-arc hybrid welded pure copper (Cu) with thickness of 2 mm was studied in detail by using different wires. The weld microstructure was analyzed, and the mechanical properties (micro-hardness and tensile property), conductivity and corrosion resistance were tested. The results showed that the alloying elements benefit the growth of column grains within weld fusion zone (FZ), increase the ultimate tensile strength (UTS) of the FZ and weld corrosion resistance, and decrease weld conductivity. The mechanisms were discussed according to the results.

Yong Xie

Papers

Anisotropy of fatigue crack growth in wire arc additive manufactured Ti-6Al-4V

Added material manufacturing method under vibration condition

A new recrystallization at semi-coherent micro-lamella and its effect on tensile properties of wire arc additive manufactured titanium alloy

Grain boundary discontinuity and performance improvement mechanism of wire arc additive manufactured Ti–6Al–4V

Effects of alloying element on weld characterization of laser-arc hybrid welding of pure copper