Directed Energy Deposition Technique Research Articles

Mechanical and Metallurgical Characteristics of Wire-Arc Additive Manufactured HSLA Steel Component Using Cold Metal Transfer Technique

Recently, the application of wire-arc additive manufacturing (WAAM) for the production of metallic products is gaining traction. WAAM is associated with the direct energy deposition technique and therefore has a higher deposition rate (approximately 4 kg/h). For this reason, it is of greater interest than powder-based additive manufacturing techniques. Industrial applications such as marine and offshore structures and pressure vessels for space programs commonly utilize high-strength low-alloy (HSLA) steel. HSLA steel components produced by casting methods exhibit defects due to oxidation. Therefore, cold metal transfer (CMT)-WAAM was adopted in this study to fabricate HSLA steel components. The metallurgical properties were analyzed using microscopic and diffraction techniques. The effects of the evolved microstructures on mechanical properties, such as strength, microhardness, and elongation to fracture, were evaluated. To analyze and test the structure, two regions were selected, namely, top and bottom. Microstructural analyses revealed that both regions were primarily composed of acicular ferrite, polygonal ferrite, and bainitic structures. The bottom region exhibited superior mechanical properties compared with the top region. The improved strength at the bottom region can be ascribed to the formation of a high density of dislocations and finer grains.

Effects of Powder Reuse and Particle Size Distribution on Structural Integrity of Ti-6Al-4V Processed via Laser Beam Directed Energy Deposition

In metal additive manufacturing, reusing collected powder from previous builds is a standard practice driven by the substantial cost of metal powder. This approach not only reduces material expenses but also contributes to sustainability by minimizing waste. Despite its benefits, powder reuse introduces challenges related to maintaining the structural integrity of the components, making it a critical area of ongoing research and innovation. The reuse process can significantly alter powder characteristics, including flowability, size distribution, and chemical composition, subsequently affecting the microstructures and mechanical properties of the final components. Achieving repeatable and consistent printing outcomes requires powder particles to maintain specific and consistent physical and chemical properties. Variations in powder characteristics can lead to inconsistencies in the microstructural features of printed components and the formation of process-induced defects, compromising the quality and reliability of the final products. Thus, optimizing the powder recovery and reuse methodology is essential to ensure that cost reduction and sustainability benefits do not compromise product quality and reliability. This study investigated the impact of powder reuse and particle size distribution on the microstructural and mechanical properties of Ti-6Al-4V specimens fabricated using a laser beam directed energy deposition technique. Detailed evaluations were conducted on reused powders with two different size distributions, which were compared with their virgin counterparts. Microstructural features and process-induced defects were examined using scanning electron microscopy and X-ray computed tomography. The findings reveal significant alterations in the elemental composition of reused powder, with distinct trends observed for small and large particles. Additionally, powder reuse substantially influenced the formation of process-induced defects and, consequently, the fatigue performance of the components.

Microstructural and mechanical properties of Al-5356 alloy structures fabricated using direct energy deposition (DED): In-pursuit to optimizing deposition parameters

Many industries including aerospace make extensive use of lightweight materials like aluminium alloys because of their extraordinary properties. Wire Arc Additive Manufacturing-Cold Metal Transfer (WAAM-CMT) as a part of modern direct energy deposition technique can be recommended for developing aerospace components of aluminium alloys. However, it is still necessary to investigate the impact of the combined change of developing parameters on some of the crucial qualities including metallurgical and mechanical properties. Therefore, in this part of research work, practically, various process parameters were tried for development of aluminium (Al-5356) alloy walls. Finaly, a specific set of parameters namely wire feed speed, scanning speed and inter layer temperature parameters with two levels of each were selected and with the assistance of these, four walls have been fabricated. Th preliminary analysis showed that low heat input accompanied by higher scanning speed of 60 cm/min and lower wire feed rate of 6 m/min was found to best suitable set of parameters for developing dimensionally stable Al wall with flaw less microstructure. The said set of parameters also showed higher hardness that also accompanied with finer grains, lower percentage towards high angle grain boundary and lower KAM. Even slight variation in these parameters that deal to high heat input can give rise of porosity and misalignment in the wall. Details of microhardness reported high hardness in the bottom part of the wall. However, in a single bead the hardness is higher in the top region, which may be owing to finer grains in the specified region. The above said set of parameters also able to deliver better tensile strength and toughness for Al-5356 alloy. The developed alloy showed improved strength in longitudinal orientation owing to intra layer failure with ductile mode of fracture in contrast to transverse orientation, where the failure mode was reported to mixed (ductile as well as brittle) owing to inter layer fracture.

Processability of K340 Cold Work Tool Steel by Directed Energy Deposition Technique

Processability of K340 Cold Work Tool Steel by Directed Energy Deposition Technique

Interfacial characteristics of Nickel-based hybrid structures fabricated using directed energy deposition

The wire-arc directed energy deposition technique was used to develop nickel-based hybrid structures or to repair conventional structures of nickel-718 superalloy. Three different cases were investigated: deposited IN718 and IN625, separately, over the conventional IN718 substrate and deposited IN718 over the previously deposited IN625 substrate. The interfacial characteristics with respect to the microstructural features, residual stresses, compositional changes, etc., were studied using a finite element computational framework and a Monte-Carlo grain growth model. The numerical results were successfully validated with the experimental results. All the hybrid structures revealed excellent interfacial bonding with no defects, as evidenced by the failures outside the interface during their tensile tests. However, the interfacial characteristics differed for each material condition. The results discussed in this study will improve the understanding of developing nickel-based hybrid structures using additive methods and can potentially be beneficial in repairing industrial components.

Influence of thermal conductivity on evolution of grain morphology during laser-based directed energy deposition of CoCrxFeNi high entropy alloys

A model CoCrxFeNi high entropy alloy system was chosen to investigate the effect of thermal conductivity on the evolution of spatial orientation of columnar grain morphology during laser directed energy deposition. The thermal conductivity of the alloy was varied by tuning the chromium content in CoCrxFeNi alloys. CoCrxFeNi alloys with chromium content ranging between 0 and 24 at% were produced under identical processing conditions of laser direct energy deposition method. Electron back scattered diffraction images of the cross-sections revealed that the spatial orientation of grain morphology transitioned from zigzag columnar grains from layer-to-layer to near-continuous columnar grains across multiple layers with increased content of chromium in CoCrxFeNi. A multi-scale multi-physics finite element based thermo-kinetic model with consideration to multi-track multi-layer nature of the laser direct energy deposition technique was adopted to correlate the process thermo-kinetics with the evolution of microstructure. The computation calculations revealed that the decrease in thermal conductivity from 36 W/m.K (CoFeNi) to 26 W/m.K (CoCr24FeNi) at the melting point reduced the cooling rate from 3.3 ×104 °C/s to 1.3 ×104 °C/s in CoFeNi and CoCr24FeNi alloys, respectively. This subsequently evolved into increased degree of remelting of previously deposited layers and caused the direction of resultant thermal gradient to reorient towards the build direction. Such reorientation in resultant thermal gradient contributed to transition of spatial orientation of grain morphology from columnar zigzag microstructures from layer-to-layer to near continuous columnar grains across multiple layers. The present observation was verified compared with other reported metallic systems exhibiting zigzag and continuous columnar grains, and a unified mechanism underlining the role of thermal conductivity on microstructure evolution was proposed.

Boosted wear and electrochemical corrosion resistance properties of Ti6Al4V alloy via graphene nanoplatelets and titanium particles

The Ti6Al4V(TC4) alloy is renowned for its robust strength, low density, exceptional resistance to corrosion, and outstanding biocompatibility, making it applicable in aviation, biomedical, and various other industries. However, its application is hindered by its inherent limited hardness and suboptimal resistance to wear. TiC, known for its compatibility with titanium alloys, serves as a frequently employed reinforcing phase in titanium matrix composites. The incorporation of TiC reinforcing phases can be classified into two categories: “in-situ” and “ex-situ”. In this research, graphene nanoplatelets (GNPs) and pure titanium (TA2) were ball-milled to produce graphene‑titanium particles, which were then utilized for the in-situ generation of TiC, and compared with the direct incorporation of nano-TiC into the titanium matrix. The deposition samples of GNPs/TA2/TC4 and nano-TiC/TA2/TC4 composites were fabricated employing the laser directed energy deposition technique. The findings of this research suggest that during the manufacturing process, the graphene nanoplatelets underwent dissolution within the molten pool. The carbon elements from the dissolved graphene nanoplatelets reacted in-situ with titanium elements, resulting in an ‘in-situ reaction’ that generated the TiC reinforcement phase. The microstructures of GNPs/TA2/TC4 and nano-TiC/TA2/TC4 deposition samples exhibit primary TiC in granular, floral, and dendritic morphologies. However, the TiC dendrites generated in situ by GNPs show shorter crystal axes. The GNPs/TA2/TC4 deposition sample displays the most pronounced grain refinement, featuring a mean grain size measuring 2.27 μm. The microhardness values of GNPs/TA2/TC4 and nano-TiC/TA2/TC4 deposition samples are (413 HV0.2 and 526 HV0.2), respectively, representing an increase of approximately 33 % and 69 % compared to the TA2/TC4 pure material deposition sample. The GNPs/TA2/TC4 deposition sample exhibits the lowest friction coefficient (0.236), indicating superior wear resistance. Moreover, the corrosion resistance of the GNPs/TA2/TC4 deposited sample is optimal (RP = 23,536 Ω cm2, Icorr = 2.03 × 10−6 A·cm−2, Ecorr = −0.703 V/SCE).

Microstructure evolution and mechanical property of melt-grown Al2O3/GdAlO3/ZrO2 eutectic ceramics prepared by laser directed energy deposition

Highly dense Al2O3/GdAlO3/ZrO2 eutectic ceramics are one-step additively manufactured by laser directed energy deposition technique under different scanning speed to investigate the inherent response relationship between processing parameter, microstructure, and mechanical property. During the layer-wise deposition process, planar-cellular transition occurs near the bottom of the molten pool, leading to the transformation of irregular eutectic structure into eutectic colony structure lengthened along the building direction, accompanied by the refinement of microstructure dimension. With the increase of scanning speed, the eutectic spacing decreases, and the initially irregular “Chinese script” eutectic ultimately transforms into hexagonally arranged rod-like eutectic structure induced by lamellar instability. The rod spacing is 1.136 times larger than the lamellar spacing. The mechanical property of the laser 3D-printed Al2O3/GdAlO3/ZrO2 eutectic ceramic is manifested as isotropic. The hardness increases with the refinement of the microstructure, while the fracture toughness decreases as the eutectic morphology transforms into rod-like structure. The averaged hardness and fracture toughness are 16.27 GPa and 3.39 MPa‧m1/2, respectively.

3D finite element analysis and experimental correlations of laser synthesized AlCrNiTiNb high entropy alloy coating

A 3D Finite Element Analysis (FEA) model of laser cladding process of AlCrNiTiNb high entropy alloy (HEA) coatings on Titanium alloy (Ti6Al4V) substrate has been developed taking into account heat transfer and free surface movement. The use of Ti6Al4V is highly evident in applications such as aerospace, automobile and marine environments due to their outstanding specific strength to weight ratio. Although they have high strength useful for fabrication of engineering components and movable parts in a mechanical system, Ti6Al4V are restricted to non-friction applications as a result of their low hardness. In this work, AlCrNiTiNb HEA hard-coating with equi-atomic ratio was synthesized on Ti6Al4V alloy substrate by laser cladding technique to mitigate the limitations. Prior to experimental method, a 3D computational model was developed to simulate the physical phenomena based on heat transfers involved during laser surface cladding (LSC) of HEA coating on Ti‐6Al‐4V alloy by a laser-assisted direct energy deposition technique. COMSOL Multiphysics 5.3a was used to create a model using heat transfer in solids module incorporating temperature distribution during the layer-wise build-up of 3 layers. The experimental validation showed that the microstructural analysis by scanning electron microscope (SEM) resulted in coating having dendritic and interdendritic structure which resulted in good metallurgical bonding. X-ray diffraction (XRD) analysis displayed that AlCrNiTiNb alloy coating is composed of ordered and disordered solid solution phases (BCC and FCC) with no intermetallic compounds formed. Energy dispersive spectrometer (EDS) confirmed the presence of elements used. The microhardness of AlCrNiTiNb HEA coating reached maximum value around 892 HV which is more than of the substrate. The microhardness increased significantly due to the combination of BCC and FCC solid solution phases.

Ceramic reinforced composite coatings on cold work tool steel fabricated by wired direct energy deposited plasma

Ceramic-based coatings are beneficial in improving the microstructural and micromechanical performance of the surface exposed to extreme conditions. Due to their high melting point and exceptional hardness, ceramic-based carbides and borides are deposited on surfaces using various techniques. In this study, the 90MnCrV8 cold work tool steel surface was coated with in situ ceramic FeW, B4C, and TiB2. The process was accomplished using plasma-transferred arc (PTA) direct energy deposition technique. The coatings' microstructural (phase structure, distribution chemical composition), micro-mechanical (microhardness, indentation modulus of elasticity, creep behavior, and plasticity indices), and tribological characteristics (wear and friction behavior) were examined. No voids, cracks, or discontinuity defects were found in the produced coatings. Ceramic particle-reinforced composite coatings have superior hardness. The highest hardness was observed in TiB2 ceramic coatings. They also outperformed as-plasma-modified coatings in terms of micro-mechanical properties. The superior toughness was measured in FeW-containing coatings (highest H3/E2 ratio), and the highest creep resistance was determined in B4C and TiB2 coatings. The indentation elasticity modules increased approximately 8 times with the ceramic reinforcement. The highest indentation elasticity modulus values were observed in boron-containing coatings. Ceramic particle-reinforced composite coatings performed 5 to 9 times improved wear resistance. The lowest Coefficient of friction (COF) was observed in the B4C coating. It was observed that the chemical affinity of B4C coatings is outstanding. B4C coatings exhibited superior micro-tribo-mechanical properties to other ceramic and as-plasma-modified coatings.

Investigating helium ion irradiation resistance in additively manufactured austenitic stainless steels

Additive manufacturing (AM) enables the rapid fabrication of complex shapes using engineering materials such as austenitic stainless steels and can imbue them with high irradiation resistance for use in reactor components. This is attributed to their refined grain structure and high grain boundary area. In this study, austenitic stainless steels (type 304) fabricated via direct energy deposition (DED) and powder bed fusion (PBF) techniques were irradiated with 5 MeV He ions to an approximate dose of 0.6 dpa at 300°C; subsequently, they were characterized through electron microscopy and the micro tensile testing. The results revealed that austenitic stainless steels manufactured using AM methods exhibited outstanding mechanical performance. The high performance of austenitic stainless steels fabricated through the DED technique can be attributed to their high tensile strength and excellent ductility elongation. This excellent performance is believed to be caused by the low stacking fault energy and the corresponding martensite formation during deformation. In particular, it was found that better mechanical properties were maintained even after helium irradiation, which is an important result obtained from the micro-tensile test. Even a small variation in the chemical composition and sub-microstructure of AM materials could result in improved irradiation tolerances.

Dynamic mechanical response and fracture behaviour of Ti–Ni–C composites fabricated by directed energy deposition

This work studied the mechanical response and the associated microstructures and failure mechanisms of additively manufactured Ti matrix composites with in-situ synthesised Ti2Ni and TiCx reinforcements under a variety of loading rates. The composites were fabricated using directed energy deposition technique with Ti–6Al–4V (Ti64) and Ni coated graphite (NCG) powders. Different proportions of Ti64 and NCG were mixed to manufacture the specimens with different compositions. Compression tests were conducted at strain rates in the range of 10−3 to 800 s−1. Our results show that the metallurgical and mechanical properties of the composites change with the NCG fraction. The failure mechanisms of the composites are a combination of tensile fracture of brittle TiCx precipitates and shear of the Ti matrix. The composites with higher NCG content exhibit increased strength, reduced ductility and less strain rate sensitivity. Under high strain rate compression loading, the Ti–Ni–C composite can provide enhanced strength with the ductility unchanged, which make it a prospective material for the applications subjected to impact loads.

Comparative Life Cycle Assessment and Cost Analysis of the Production of Ti6Al4V-TiC Metal–Matrix Composite Powder by High-Energy Ball Milling and Ti6Al4V Powder by Gas Atomization

Environmental awareness and the necessary reduction in costs in industrial processes has facilitated the development of novel techniques such as Additive Manufacturing, decreasing the amount of raw materials and energy needed. The longing for improved materials with different and enhanced properties has resulted in research efforts in the Metal Matrix Composites field. These two novelties combined minimise environmental impacts and costs without compromising technical properties. Two technologies can feed Additive Manufacturing techniques with metallic powder: Gas Atomization and High Energy Ball Milling. This study provides a comparative Life Cycle Assessment of these technologies to produce one kilogram of metallic powder for the Directed Energy Deposition technique: a Ti6Al4V alloy, and a Ti6Al4V-TiC Metal–Matrix Composite, respectively. The LCA methodology is according to ISO 14040:2006, and large amounts of information on the use of raw materials, energy consumption, and environmental impacts is provided. Different impact categories following the Environmental Footprint methodology were analysed, showing a big difference between both technologies, with an 87.8% reduction of kg CO2 eq. emitted by High Energy Ball Milling in comparison with Gas Atomization. In addition, an economic analysis was performed, addressing the viability perspective and decision making and showing a 17.2% cost reduction in the conventional process.

Powder catchment efficiency in laser cladding (directed energy deposition). An investigation into standard laser cladding and the ABA cladding technique

This paper investigates the efficiency of powder catchment in blown powder laser cladding (a directed energy deposition technique). A comparison is made between standard “track by overlapping track” cladding (“AAA” cladding) and “ABA” cladding, where the gaps left between an initial set of widely spaced tracks (“A” tracks), are filled in by subsequent “B” tracks. In both these techniques, the melt pool surface is the collection area for the cladding powder, and the shape of this pool can be affected by several parameters including cladding speed, intertrack spacing, and type of cladding technique. The results presented here are derived from of an analysis of high-speed videos taken during processing and cross sections of the resultant clad tracks. The results show that the first track in AAA cladding has a different melt pool shape to subsequent tracks, and that the asymmetry of the subsequent track melt pools results in a reduction in the powder catchment efficiency. In contrast to this, the geometry of the “B” track melt pools between their adjacent “A” tracks results in an enhanced powder catchment efficiency.

Study of laser directed energy deposition of Inconel 625 and austenitic steel

Functionally graded material (FGM) is an advanced material that illustrates the number of properties in a single component. To develop FGM, it is very important to study each component gradient separately to understand the properties and their behaviour. This paper presents the study of the properties of deposited blocks of the different gradients of Inconel 625 (IN625) and stainless steel 304L (SS304L) (25% IN625 + 75% SS304L, 50% IN625 + 50% SS304L, 75% IN625 + 25% SS304L, and 100% IN625) by a laser directed energy deposition technique. Various tests were performed to understand its mechanical, metallurgical, and chemical behaviour. Deposited samples were heat-treated and then optical microscopy and microhardness were measured and compared to untreated ones and results found to be comparatively improved.

Corrosion-erosion behavior and mechanism of Cu[sbnd]Mo co-doped CoCrFeNi high-entropy alloy coating prepared by directed energy deposition

Developing cost-effective and high-performance high-entropy alloy (HEA) coatings on demand is imperative. This study designed a class of HEAs on-demand by synergistic doping of Cu and Mo elements based on the first-principles and multi-principal alloy design concept. A CoCrFeNiCu0.25Mo0.75 HEA coating with outstanding corrosion and slurry erosion wear performances was fabricated on the duplex stainless steel using the directed energy deposition technique. The corrosion mechanism of the HEA coating in 3.5 % NaCl and 0.5 M H2SO4 solutions and the slurry erosion wear mechanism under a slurry concentration of 5 wt% were analyzed in combination with the density functional theory. The results indicate that the SQS crystal model is a better predictor of phases and properties of HEA than the VCA model. The HEA coating is a cellular structure that consists mainly of a face-centered cubic phase structure and contains a small amount of homogeneous sigma nanocrystalline secondary phase precipitation. Meanwhile, the passive film of the HEA coating is mainly composed of metal oxides and hydroxides. Cu is not oxidized during the corrosion process and always exists in the metallic form, which serves as a barrier layer to prevent the transfer of point defects. Mo with a larger atomic size can induce lattice distortion, enhance the coating strength and hardness, and reduce the density of point defects. Further, the slurry erosion wear rate of the HEA coating is lower at a 30° impingement angle than 90° for brittle erosion mode. At the 30° impingement angle, micro-cutting and ploughing are the main wear mechanisms of the HEA coating, while at the 90° impingement angle, micro-indents and craters are the main wear mechanisms. In addition, the corrosion and slurry erosion wear performances of CoCrFeNiCu0.25Mo0.75 HEA coating are better than the most reported once-formed HEAs.

Effect of microsegregation behaviors on solidification microstructure of IC10 superalloy fabricated by directed energy deposition

Due to the solidification process and thermal history, the microstructure and properties along the deposition direction are generally inhomogeneous in components fabricated by the directed energy deposition technique. By developing a microsegregation model, this study gives an innovative understanding of the elemental segregation behavior of an as-deposited IC10 superalloy along the different heights and its influence on the microstructure. Results indicate that the γ-γ ´ eutectic-free microstructure is only obtained at the initial deposition layer, and as the deposition height increases, eutectic phases gradually appear in interdendritic regions. By taking account of the nonequilibrium solidification and dendritic tip undercooling, the new microsegregation model can well explain the segregation behavior of the alloy at different deposition heights. Compared to the back diffusion coefficient, the partition coefficient plays a major role in microsegregation behavior under rapid solidification conditions, especially for the elements with a high diffusion coefficient in solid, such as Ti and Al. Moreover, microstructure transformation is dependent on varying solidification processes due to the change in microsegregation. Limited by the heat transfer efficiency as the increased deposition heights, the temperature gradient and solidification rate decrease, which exacerbates the enrichment of Al and Ti at interdendritic regions and promotes the eutectic phase nucleation. Restricted by the diffusion rate of alloying elements, the eutectic reaction rate slows down, γ and γ ´ lamellae thickness increase, and finally the petal-like eutectic phases form.

Evolutions of microstructure and mechanical property of high nitrogen steel repaired by the underwater directed energy deposition technique

Damaged high nitrogen steel (HNS) plates were repaired by underwater laser direct metal deposition (UDMD) technique at the ambient pressure of 0.3 MPa. Both experiments and finite element method (FEM) simulations were employed to elucidate the influence mechanism of the underwater hyperbaric environment on the microstructure evolution. Carbides were the most typical precipitates in the HNS selected in this research, and their features were dominated by molten pool cooling rate and the intrinsic heat treatment (IHT) effect associated with the thermal cycles. Accelerated cooling rate induced by water chilling effect or the weakened laser energy input promoted the carbide precipitation. Against the build direction, carbides became coarse and the overall content decreased due to the cumulative IHT effect. Such carbide features evolution trend in UDMD repaired sample was more pronounced than that in DMD repaired sample. The shortened high-temperature duration owing to the intense thermal dissipation in the underwater environment highlighted the proportion of intrinsic heat treatment (IHT) effect on carbide features and dendrite size. Owing to the slow air cooling and enhanced thermal accumulation in the ground environment, the prolonged high-temperature duration facilitated the decomposition of unstable austenite into lamellar intragranular carbide and ferrite. Benchmarking mechanical properties against the DMD repaired sample counterpart demonstrated that UDMD repaired samples possessed higher strength and comparable impact toughness.

Nanoindentation and Corrosion Behaviour of 410 Stainless Steel Fabricated Via Additive Manufacturing

This study investigates the microstructural, nanomechanical, and corrosion behaviour of different sections of 410 steel fabricated via directed energy deposition technique. The morphology exhibited by the longitudinal and transverse sections of the specimens was examined under a scanning electron microscope (SEM), while micro-computed tomography technique (micro-CT) was used for examination of the internal structure of the specimens. Nanomechanical properties were assessed using a nanoindenter, while potentiodynamic polarization technique was adopted to investigate the corrosion resistance of the specimens in a chloride environment. The SEM micrographs revealed minimal pores in the specimens which confirmed the improved density in the layer-by-layer built specimen. Micro-CT images confirmed the presence of tiny pores in the specimens sectioned from the top layer of the 410 stainless steel rod in comparison with the middle- and bottom-sectioned specimens. The corrosion and post-corrosion analyses confirmed that the top specimen exhibits the least corrosion resistance in comparison with the other specimens.

Microstructure characterization of gradient composition between TC25G and TiAl alloys prepared by directed energy deposition technique

Graded Materials are now used widely as structural components due to their specific properties. Researching on microstructure evolution of the transition region in graded materials is important to control the entire property of the graded materials. In this study, three alloys with the typical compositions were made by directed energy deposition (DED), which were correlated to the transition zone of the TC25G/TiAl graded material. Results indicate that the DEDed TiAl alloy consists of a duplex microstructure with γm and (α2 + γ) lamellar. For sample AD75 (mixed of 75 wt% TiAl and 25 wt% TC25G powder), the microstructure changes to B2 + α + γm + (α2 + γ). The continuing increase of TC25G alloy content causes the microstructure transfer to β/B2 + α + ω + (α + α2) and β + α + (α + α2) for sample AD50 (mixed of 50 wt% TiAl and 50 wt% TC25G powder) and AD25 (mixed of 25 wt% TiAl and 75 wt% TC25G powder) alloy consequently. Besides, the microstructure of TC25G alloy is β + α + α2. The highest hardness is found in AD75 alloy, followed by AD50, TC25G, AD25 and TiAl alloy, which is attributed to a large amount of B2 and α2 phase formation.