In this paper, the microstructure, and mechanical properties of Ti-6Al-4V fabricated through Laser Directed Energy Deposition (L-DED) process are investigated and discussed. Deposited coupons were produced on Ti-6Al-4V wrought substrate using Ti-6Al-4V ELI grade wire with the laser wire deposition (LWD) process. Characterization efforts led to the evaluation of the microstructure, hardness, tensile behavior, and fatigue crack growth resistance of the build-up alloy. Microstructure of the deposit consists of columnar prior β grains and basket-weave α/β phase mixture. The size of the alpha laths is measured as 1.2 ± 0.3 µm and 0.8 ± 0.2 µm in the banded zone and band-free zone, respectively. Hardness of the deposited block is found to be uniform and ranging between 321 and 323 Hv. Tensile and fatigue crack growth properties of the deposited block were evaluated in various orientations. Tensile specimens loaded in the deposition direction exhibited 824 MPa and 930 MPa for yield and ultimate tensile strength, respectively. Tensile specimens loaded in the build direction exhibited 782 MPa and 907 MPa for yield and ultimate tensile strength, respectively. The analysis reveal that the tensile properties of the deposited material match the strength requirements for ASTM F1108 Cast Ti-6Al-4V. However, they fell just below the AMS 4911P Wrought Ti-6Al-4V standard. Fatigue Crack Growth Rate tests were conducted for three directions: parallel to the deposition direction, parallel to the build direction and at 45° of the deposition direction. No significant differences in crack growth properties were observed between the different orientations with average crack initiation near threshold (ΔKth) and the fracture toughness (Kc) value of 3.6 MPa√m and 69 MPa√m, respectively. The crack propagation properties are similar to cast & wrought materials.

Following foreign object damage (FOD), a decision to repair components using novel additive manufacturing (AM) technologies has good potential to enable cost-effective and efficient solutions for aircraft gas turbine engine maintenance. To implement any new technology in the gas turbine remanufacturing world, the performance of the repair must be developed and understood through careful consideration of the impact of service life-limiting factors on the structural integrity of the component. In modern gas turbine engines, high cycle fatigue (HCF) is one of the greatest causes of component failure. However, conventional uniaxial fatigue data is inadequate in representing the predominant HCF failure mode of gas turbine components that is caused by vibration. In this study, the vibratory fatigue behavior of Ti6Al4V deposited using wire-fed electron beam additive manufacturing (EBAM) was examined with the motivation of developing an advanced repair solution for fatigue critical cold-section parts, such as blades and vanes, in gas turbine engine applications. High cycle fatigue data, generated using a combination of step-testing procedure and vibration (resonance) fatigue testing, was analyzed through Dixon–Mood statistics to calculate the endurance limits and standard deviations of the EBAM and wrought Ti6Al4V materials. Also plots of stress (S) against the number of cycles to failure (N) were obtained for both materials. The average fatigue endurance limit of the EBAM Ti6Al4V was determined to be greater than the wrought counterpart. But the lower limit (95% reliability) of 426 MPa for the EBAM Ti6Al4V was lower than the value of 497 MPa determined for wrought Ti6Al4V and was attributed to the slightly higher data scatter–as reflected by the higher standard deviation–of the former material.

The effect of rare-earth (Sm) microalloying on the thermal stability and phase selection along with the effect of nanocrystallization on the mechanical properties of amorphous melt-spun ribbons of Zr50Cu40Al10, Zr49Cu39.2Al9.8Sm2 and Zr48Cu38.4Al9.6Sm4 alloys were investigated using differential scanning calorimetry (DSC), X-ray diffraction (XRD), transmission electron microscopy (TEM), Vickers and nanoindentation hardness tests and micropillar compression analysis. XRD and TEM analyses showed that all samples were fully amorphous in as-spun state; however, crystallization sequences for the Sm-free and the Sm micro-alloyed samples were different during devitrification. Combined study of XRD, DSC and TEM on melt-spun ribbons show that Zr48Cu38.4Al9.6Sm4 have nanocrystallization of Cu2Sm phase with an average diameter of 10 nm, which was absent in Zr50Cu40Al10, prior to crystallization of Cu10Zr7 phase. The nanoindentation and micropillar compression tests revealed Cu2Sm nanocrystals embedded in Zr48Cu38.4Al9.6Sm4 alloy improves strength and hardness. On the other hand, presence of these nanocrystals deteriorate shear band stability and thus result in a catastrophic brittle fracture through a single shear band burst.

The effect of Sm micro-alloying on non-isothermal and isothermal crystallization kinetics of (Zr50Cu40Al10)(100-x)Sm-x (x = 0, 2, 4 at. % Sm) alloys were investigated using differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and X-ray diffraction (XRD). Crystallization activation energies for each composition were calculated in non-isothermal conditions using Kissinger and Ozawa methods and in isothermal conditions using Johnson-Mehl-Avrami model. XRD analysis showed that crystallization product Cu10Zr7 changes to Cu2Sm with Sm presence in isothermal conditions. Both isothermal and isochronal calculations yield that the energy barrier for crystallization has increased with Sm addition. On the other hand, crystallization point drops to lower temperature at the expense of an increase in the pre-exponential factor. The Avrami exponents for all compositions were found to be below 2.5, indicating that crystallization was governed by a diffusion-controlled three-dimensional growth with a decreasing nucleation rate. The apparent increase in crystallization activation energies with increasing Sm content can be one of the affecting factors for commonly held idea of increased glass forming ability for rare-earth containing Zr-based metallic glasses.

This study focuses on the impact properties of Ti–6Al–4V produced by LPBF using un-notched Charpy impact testing. The effects of the build orientation, impact orientation, and half stress-relief and hot isostatic press (HIP) heat treatments on the impact resistance were investigated. The impact properties of HIPed samples were significantly greater than those of stress-relieved ones. Microstructural analysis and fractography revealed that process defects such as porosity, and columnar grain boundaries play an important role in crack initiation and propagation in the stress-relieved samples. In the HIPed samples the orientation of prior-β grain boundaries with respect to the impact loading, and impact energy absorption by microstructural modification from the high strains promoting formation of globular α were the main contributors in the impact resistance of the samples. Consequently, the vertically-built HIPed samples demonstrated the greatest impact energy from the combination of the perpendicular prior-β grain boundaries to the impact and highest observed α globularization.