Additive Manufactured Alloy Research Articles

Current Research Situation and Prospect of Wire and Arc Additive Manufacturing of Titanium Alloy

Wire arc additive manufacturing is an important part of additive manufacturing. Because of its low processing cost, high forming efficiency, high material utilization rate and low equipment cost, it is favored in the fields of medical and aerospace. This paper briefly discuss the technologies of titanium alloy wire arc additive manufacturing. The influence of different deposited parameters, interpass rolling, ultrasonic assistance and heat treatment on the forming quality of titanium alloy wire arc additive components are summarized and analyzed. Finally, combined with the actual engineering requirements, the problems and research directions of the development of titanium alloy additive manufacturing are analyzed.

Comparison of Bond Strength Between Two Resin Cement Types and Additive Manufacturing or Cast Cobalt-Chromium Alloys.

To compare the bond strength of two types of resin cement to that of additive manufacturing (AM) or cast cobalt-chromium (Co-Cr) alloys. Two types of resin luting cement, composite resin and methyl methacrylate (MMA), were bonded to AM or cast Co-Cr alloys, and shear bond tests were performed after seven days of storage in distilled water at 37°C. Co-Cr alloy adhesive elements AM to the enamel surface of the labial aspect of a bovine mandibular central incisor crown were bonded with two types of resin luting cement and subjected to 1,000 cycles of storage in water for one day and 28 days or thermal cycling, followed by shear bonding tests. Residual cement on the metal and enamel surfaces after the bonding tests was evaluated using an optical microscope. The normality of the results was evaluated using statistical software Statcel4, analysis of variance, or Kruskal-Wallis test, depending on normality, and multiple comparison tests were performed using the Tukey-Kramer or Steel-Dwass tests. After one day, the shear bond strength (SBS) was 25.9 MPa for Panavia V5 (PV; Kuraray Noritake Dental Corporation, Niigata, Japan) and 23.5 MPa for Super-Bond (SB; Sun Medical Corporation, Shiga, Japan), with no significant difference between the two cement types (P > 0.05). After 28 days, the SBS decreased to 4.1 MPa for PV and 6.7 MPa for SB, showing a significant difference between the two cements (P < 0.05). Following 1,000 thermal cycles, the SBS was 2.0 MPa for PV and 5.6 MPa for SB, with SB exhibiting a significantly higher value (P < 0.05). The adhesive strength was significantly lower after 28 days of storage and thermal cycling compared to after one day of storage (P < 0.05). The Co-Cr alloy exhibited more residual cement on the enamel surface due to interfacial fracture with the resin cement. The Co-Cr alloy showed more residual cement on the enamel surface due to interfacial fracture with the resin cement. MMA-based resin cement showed optimal bond strength and may be suitable for clinical use in computer-aided design (CAD)/computer-aided manufacturing (CAM) orthodontic appliances.

Numerical simulation of surface roughness effects on low-cycle fatigue properties of additively manufactured titanium alloys

Additive manufacturing (AM) is a complex process involving a multiscal physical phenomena (solid–liquid-gas), often resulting in poor surface quality. Although surface treatments such as polishing or chemical treatment can improve surface quality, localized sub-grain stress concentrations induced by surface roughness anomalies are still easily formed, which can lead to the reduction and dispersion of fatigue properties in AM alloys. In this study, a numerical simulation model is proposed to study the association between surface roughness and fatigue properties of AM alloys. Based on the continuum damage mechanics modeling framework, an idealised grain/grain boundary model is generated by employing the Voronoi tessellation meshing technology. The numerical simulations are performed for the model with different surface geometric states. The correlation between surface roughness geometric features and fatigue properties is analyzed and discussed. A parameter “G” which comprehensively considers the influence of the maximum surface height (Rz) and correlation length (Lcor) is proposed to quantify the influence of surface roughness geometric features on the fatigue properties of AM alloys. This finding can be of great significance in improving the surface integrity of components to increase service life.

The influence of additive manufacturing on Portevin-Le Châtelier (PLC) effect in Ni–Co-based superalloy

The microstructures and tensile properties of the Ni–Co-based superalloys made by additive manufacturing (AM) were investigated. The results revealed that both normal and inverse Portevin-Le Châtelier (PLC) effects were observed in AM Ni–Co-based superalloys. In addition, AM significantly inhibited the PLC effect, the average stress decrements for the cast and wrought (C&W) alloys with the same nominal compositions were more than ten times as large as those for the AM alloys when tested at 400 °C with a strain rate of 3 × 10−4 s−1. In the AM Ni–Co-based superalloys, type C serrations had connections with the inverse PLC effect. Transmission electron microscope (TEM) was performed to investigate the interactions of solute atoms, dislocations, stacking faults (SFs) and the γ′ phase for a deep insight into mechanisms of the PLC effects and clarifying the changes in serration types and the conversion from normal to inverse PLC effect.

Microstructure and properties of Al–Zn–Mg–Cu alloy fabricated by cold metal transfer additive manufacturing

Al–Zn–Mg–Cu alloy additive manufacturing components were fabricated by cold metal transfer advance (CMT-A) and metal inert-gas welding (MIG). The results indicate that the CMT-A as-deposited sample has fine grains with small-sized η'-strengthened precipitates and supersaturated solid solution, and the hardness is increased by 16.1% compared to the MIG as-deposited sample, and its peak aging hardness increased by 36.8% compared to the MIG. It indicates that CMT-A can directly produce Al–Zn–Mg–Cu products that have the potential to achieve high strength without the need for re-solutionizing.

Enhanced Plastic Stability: Achieving High Performance in a Al6xxx Alloy Fabricated by Additive Manufacturing.

Additive manufacturing (AM) facilitates the creation of materials with unique microstructural features and distinctive phenomena as compared to conventional manufacturing methods. Among the various well-fabricated AM alloys, aluminum alloys garner substantial attention due to their extensive applications in the automotive and aerospace industries. In this work, an Al6xxx alloy is successfully fabricated with outstanding performance. A nucleation agent is introduced to diminish the susceptibility to cracking during the AM process, thereby inducing a heterogeneous microstructure in this alloy. However, the introduction of ultrafine grains induces plastic instability, evidenced by the presence of Lüders band. This work investigates the evolution of the Lüders band and the strategy to reduce their undesirable effect. The heterogeneity destabilizes the band propagation and thus deteriorates the ductility. Through a T6 heat treatment, the local Lüders strain decreases from 10.0% to 6.2%, leading to a substantial enhancement in plastic stability. With the increase in grain growth and the enlargement of coarse grain regions, the mismatch between the local and macroscopic Lüders strain disappears. Importantly, the strength and the thermal conductivity are concurrently increased. The findings demonstrate the significance of ensuring plastic stability to achieve improved strength-ductility trade-off in AM alloys with heterogeneous microstructures.

Microstructure evolution and mechanical property enhancement of friction stir additive manufactured Ti6Al4V alloy

Friction stir additive manufacturing (FSAM) is a promising and cost-effective technology that has found extensive applications in the fabrication of lightweight alloy components, particularly aluminum and magnesium. However, the exploration of FSAM for titanium alloys is still at an early stage. In this study, the microstructure evolution and mechanical properties of the dual-phase Ti6Al4V alloy fabricated by FSAM were investigated. The microstructural characteristics under various process parameters were determined using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The experimental findings revealed that the stir zone (SZ) exhibited a refined and equiaxial grain structure with a gradient microstructure when the tool rotation speed was set at 150 rpm and the travel speed at 50 mm/min, which was attributed to the combined effects of mechanical fragmentation and dynamic recrystallization (DRX) behavior. Moreover, upon employing a tool rotation speed of 300 rpm and a travel speed of 100 mm/min, acicular products were observed in conjunction with lamellar (α+β) structures located at both the top and center regions within the SZ. The microhardness and tensile properties were improved after FSAM treatment (150 rpm-50 mm/min). Furthermore, the dominant mechanisms of microstructure evolution as well as mechanical property enhancement in friction stir additive manufactured (FSAMed) Ti6Al4V were revealed, thereby providing valuable insights for titanium alloy additive manufacturing processes.

High fatigue resistance in a titanium alloy via near-void-free 3D printing.

The advantage of 3D printing-that is, additive manufacturing (AM) of structural materials-has been severely compromised by their disappointing fatigue properties1,2. Commonly, poor fatigue properties appear to result from the presence of microvoids induced by current printing process procedures3,4. Accordingly, the question that we pose is whether the elimination of such microvoids can provide a feasible solution for marked enhancement of the fatigue resistance of void-free AM (Net-AM) alloys. Here we successfully rebuild an approximate void-free AM microstructure in Ti-6Al-4V titanium alloy by development of a Net-AM processing technique through an understanding of the asynchronism of phase transformation and grain growth. We identify the fatigue resistance of such AM microstructures and show that they lead to a high fatigue limit of around 1 GPa, exceeding the fatigue resistance of all AM and forged titanium alloys as well as that of other metallic materials. We confirm the high fatigue resistance of Net-AM microstructures and the potential advantages of AM processing in the production of structural components with maximum fatigue strength, which is beneficial for further application of AM technologies in engineering fields.

Fretting and Fretting Corrosion Behavior of Additively Manufactured Ti-6Al-4V and Ti-Nb-Zr Alloys in Air and Physiological Solutions.

Additive manufacturing (AM) of orthopedic implants has increased in recent years, providing benefits to surgeons, patients, and implant companies. Both traditional and new titanium alloys are under consideration for AM-manufactured implants. However, concerns remain about their wear and corrosion (tribocorrosion) performance. In this study, the effects of fretting corrosion were investigated on AM Ti-29Nb-21Zr (pre-alloyed and admixed) and AM Ti-6Al-4V with 1% nano yttria-stabilized zirconia (nYSZ). Low cycle (100 cycles, 3 Hz, 100 mN) fretting and fretting corrosion (potentiostatic, 0 V vs. Ag/AgCl) methods were used to compare these AM alloys to traditionally manufactured AM Ti-6Al-4V. Alloy and admixture surfaces were subjected to (1) fretting in the air (i.e., small-scale reciprocal sliding) and (2) fretting corrosion in phosphate-buffered saline (PBS) using a single diamond asperity (17 µm radius). Wear track depth measurements, fretting currents and scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) analysis of oxide debris revealed that pre-alloyed AM Ti-29Nb-21Zr generally had greater wear depths after 100 cycles (4.67 +/- 0.55 µm dry and 5.78 +/- 0.83 µm in solution) and higher fretting currents (0.58 +/- 0.07 µA). A correlation (R2 = 0.67) was found between wear depth and the average fretting currents with different alloys located in different regions of the relationship. No statistically significant differences were observed in wear depth between in-air and in-PBS tests. However, significantly higher amounts of oxygen (measured by oxygen weight % by EDS analysis of the debris) were embedded within the wear track for tests performed in PBS compared to air for all samples except the ad-mixed Ti-29Nb-21Zr (p = 0.21). For traditional and AM Ti-6Al-4V, the wear track depths (dry fretting: 2.90 +/- 0.32 µm vs. 2.51 +/- 0.51 μm, respectively; fretting corrosion: 2.09 +/- 0.59 μm vs. 1.16 +/- 0.79 μm, respectively) and fretting current measurements (0.37 +/- 0.05 μA vs. 0.34 +/- 0.05 μA, respectively) showed no significant differences. The dominant wear deformation process was plastic deformation followed by cyclic extrusion of plate-like wear debris at the end of the stroke, resulting in ribbon-like extruded material for all alloys. While previous work documented improved corrosion resistance of Ti-29Nb-21Zr in simulated inflammatory solutions over Ti-6Al-4V, this work does not show similar improvements in the relative fretting corrosion resistance of these alloys compared to Ti-6Al-4V.

Integration of additive manufacturing and thermomechanical processing toward a hybrid production route for PH13-8Mo stainless steel

In the current study, PH13–8Mo is fabricated using laser-powder bed fusion and arc-directed energy deposition additive manufacturing (AM) processes. The microstructure and mechanical properties in the as-built and isothermally heat-treated conditions are studied. The isothermal heat treatment includes direct aging at 530 °C to form β-NiAl precipitates. The AM alloys (in the as-built condition) are then thermomechanically processed at the isothermal aging temperature to promote dynamic aging and dislocation multiplication. The resulting mechanical properties are found to be superior to the heat-treated conditions and correlated to the microstructure. This study paves the pathway toward developing a novel hybrid manufacturing route to fabricate alloys with exotic mechanical properties.

Progress in copper alloy additive manufacturing technology

Progress in copper alloy additive manufacturing technology

Investigation on the evolution of deposition layer grain structure and its effect on mechanical properties in aluminum alloy fabricated by laser directed energy deposition

In recent years, aluminum alloy additive manufacturing has played a significant role in promoting lightweight applications in aerospace and automotive industries due to its efficiency and cost advantages. In order to study the evolution of grain structure in the deposition layer, single-variable single-pass deposition experiments was conducted to optimize the process parameters of laser directed energy deposition (LDED). Subsequently, multi-layer multi-pass depositions were performed to fabricate the components. The deposition layer was divided into three distinct regions: Top coarse grain zone (TCZ), Central equiaxed grain zone (CEZ), and Bottom columnar grain zone (BCZ). It was observed that subsequent depositions led to recrystallization, resulting in the refinement of the original equiaxed grain region and the coarsening of the grain structure in the deposition layer, leading to the formation of the latter two characteristic grain regions. Interestingly, within the TCZ and BCZ, we observed the presence of aluminum alloy twins that are difficult to form. This observation may be attributed to a significant reduction in the required twin shear stress within the coarse grains. The stress concentration at the grain boundaries of the coarse grains and the rapid strain rate during the LDED process could also be contributing factors to the formation of aluminum alloy twins. In terms of mechanical properties, the tensile strength of the samples parallel to the deposition direction is 268.25 MPa, while the tensile strength of the samples perpendicular to the deposition direction is 276.68 MPa. The fracture surfaces exhibit numerous equiaxed dimples, displaying characteristics of ductile fracture. There is almost no anisotropy observed in the mechanical properties, this is attributed to the alternating arrangement of different crystal regions within the deposition layer and the role of twins in suppressing dislocation motion.

Microstructure and mechanical properties of AlTiCrFe and AlTiCrCu alloys processed by Laser Powder Bed Fusion

Additive manufacturing (AM) of aluminium alloys urges new alloy compositions to meet the requirements for high-strength and processability of the engineering products. This research focuses on the development of two Al alloys, AlTiCrFe and AlTiCrCu, with the goal to exploit the potential of transition element additions for grain refinement and increasing strength. Robust processability and build rates are reached for the two alloys, with no cracks and high density up to 99.8%. AlTiCrFe shows a bimodal microstructure, with the presence of ultrafine and fine grained zones, that can be attributed to a dual precipitation stage. Al3Ti precipitates are present in the ultrafine grained zone, confirming the effectivity of Ti as grain refiner. In addition, Al6Fe precipitates are present in the fine grained region, as a consequence of the later precipitation stage. AlTiCrCu, on the contrary, shows an homogeneous ultrafine grain microstructure, with Cu segregating at the grain boundaries. SAED analyses confirm the phase identification with the presence of high volume density cubic precipitates of Al3Ti_L12. AlTiCrFe and AlTiCrCu exhibit a yield strength value of 363 ± 1 MPa and 340 ± 1 MPa, respectively. These findings indicate that the two alloys open up new possibilities for a novel class of aluminium alloys for AM, leveraging the incorporation of transition elements, which aids in achieving strength during the as-built state, eliminating the requirement for supplementary heat treatment.

New patents for AM alloys

Three new patents secured for proprietary alloys specifically designed for additive manufacturing (AM).

High-Throughput Simulations of Phase Precipitation in Additively Manufactured Al Alloy

Additive manufacturing (AM) provides numerous advantages compared to conventional manufacturing methods, such as high design freedom and low material waste. Among the available materials, precipitation-hardenable aluminum alloys are highly attractive for AM due to their high specific strength and low density. Precise control of the processing conditions during AM and post heat treatment (HT) is required to tailor the final mechanical properties. Consequently, many variables, such as the chemical composition and process and HT parameters, must be considered to design suitable alloys for AM. Experimental investigations are, however, limited in variation of these variables. Therefore, computational alloy design approaches allowing for a faster evaluation of many possible variations must be developed. This work presents a high-throughput approach to determine the precipitation kinetics and thermodynamic properties based on the CALculation of PHAse Diagrams (CALPHAD) method. The developed approach is successfully validated for an Al-Mg-Si-Ti-Fe alloy and is applied to screen 243 combinations of chemical compositions and HT parameters. The results confirm the microstructural stability of the Al-Mg-Si-Ti-Fe system to small composition variations.

Enhancement of surface characteristics of additively manufactured γ-TiAl and IN939 alloys after laser shock processing

The enhancement in laser technology opened up new methods such as additive manufacturing (AM) of metals. While AM offers high design flexibility and reduced material usage, it can also produce problematic parts due to poor surface quality. A variety of post-processing techniques are available to address the drawbacks associated with the surface properties of AM. Laser Shock Processing (LSP) is one of the unique methods that induces compressive residual stress (CRS) on the surface and subsurface by creating severe plastic deformation. In this study, two critical aerospace alloys (γ-TiAl and IN939) were manufactured through two different methods called Powder Bed Fusion with Electron Beam (PBF-EB) and Powder Bed Fusion with Laser Beam (PBF-LB). Subsequently, AM samples were investigated to observe single layer LSP effects on the surface. The results of the laser peening process were determined by residual stress, microhardness and surface roughness measurements. The residual stress profiles showed that LSP significantly induces CRS on the surfaces of AM alloys. For the γ-TiAl and IN939 samples, the maximum values of CRS and depth of CRS were −460 MPa/1000 µm and −516 MPa/700 µm, respectively. Similarly, the microhardness of the materials was increased by 44.4 % for γ-TiAl and 18.2 % for IN939 by laser post-processing. In addition, a comparison of the roughness of the unground and ground AM samples was carried out. Depending on the surface condition of the AM samples, LSP had different outcomes. For example, the extreme roughness of the AM samples was partially reduced by the thermal effects of the high-energy laser shots. When comparing the roughness values in terms of Ra and Rz, there were decreases in the range of 14.7–21.3 % and 3.34–39.3 % for unground IN939 samples. However, for unground γ-TiAl samples, depending on the direction of measurement, roughness variations were observed as a 0.99 % decrease − 5.3 % increase for Ra and a 2.2 % decrease − 14.2 % increase for Rz. The roughness values for ground samples of both alloys were drastically increased, varying between 42.1 % and 7x increase. Sa values were recorded on unground AM samples. For IN939 and γ-TiAl samples these values decreased by 8.41 % and 15.8 % respectively.

Design and Characterization of Innovative Gas-Atomized Al-Si-Cu-Mg Alloys for Additive Manufacturing

Metallic powders are widely utilized as feedstock materials in metal additive manufacturing (MAM). However, only a limited number of alloys can currently be processed using these technologies, with most of them being casting alloys. The objective of this study is to investigate novel aluminum alloys produced via a close-coupled gas atomizer (CCGA) by adding an increasing amount of copper (4, 8, and 20 wt%) to an AlSi10Mg alloy. The obtained powders were fully characterized to evaluate the effect of copper, a well-established strengthener for aluminum alloys, in order to correlate the obtained hardness to the powder phase composition and microstructure. In particular, a dendritic microstructure was observed in all alloys, and, as the copper content was increased, the size of the secondary dendrite arm spacing (SDAS) decreased progressively. Consequently, the hardness measured on the powder cross-section linearly increased with the copper content, and the hardness value of 185 ± 13 HV of the AlCu20Si10Mg composition was found to be twice that of the AlSi10Mg alloy (88 ± 5 HV).

The effect of scanning strategies on the microstructure and mechanical properties of M2052 alloy manufactured by selective laser melting

To control the microstructure and improve the mechanical properties of Mn–Cu alloy additive manufacturing components, this work adopts various scanning strategies (rotations of 0°, 45°, 67°, and 90° between successive layers) to change the heat input distribution and heat dissipation. The results show that the scanning strategies can impact the porosity, cracks, grain size, and grain growth direction of Mn–Cu alloy additive manufacturing parts. By adjusting scanning strategies to change the heat flow direction the columnar-to-equiaxed transition can be achieved. The samples exhibit minimal cracks and pores (porosity of 0.0006 %). Using a scanning rotation angle of 67° during processing, the maximum tensile strength can reach 510 MPa with a 29 % elongation, attributed to effective grain refinement and a high dislocation density. This study demonstrates the feasibility of grain refinement and improved mechanical properties for the Mn–Cu alloys by changing the scanning strategies.

High conductive copper alloys for additive manufacturing

For applications where high thermal and/or electrical conductivity combined with reasonably high strength is required, copper alloys may be used. Although many different alloys were already developed in the past, additive manufacturing like laser powder bed fusion (PBF-LB/M) opens up new possibilities for alloy development, mainly driven by the very high cooling rates. This allows for the usage of precipitation-hardened alloys with compositions exceeding the maximum solubility. The present work focuses on the investigation of a well-known CuCr1Zr alloy as well as CuZr alloys with 1 and 2 wt.% Zr. For a fast, resource-efficient screening and demonstration of feasibility, the investigated alloys were not printed from powder. Instead, solid sheets were partially re-melted in a PBF-LB/M machine to obtain a microstructure similar to the printed state. This rapid-solidification microstructure is investigated, and precipitates with a size 50 nm or even smaller are found. After subsequent aging heat treatments, the hardness of the alloys exceeds the maximum hardness achievable with conventional manufacturing methods (excluding work hardening). The investigations in this work revealed the great hardening potential of these alloys for usage in the PBF-LB/M process.

Sustainable Powder-Based Additive Manufacturing Technology

A thorough exploration of sustainability in powder-based additive manufacturing (AM) is presented. This review focuses particularly on the design of sustainable alloys for AM. Environmental, economic, and social aspects of sustainability are covered. The importance of life cycle assessment (LCA) in evaluating environmental impact is discussed. LCA tools are used to analyse factors such as energy consumption, waste management, and air pollution, providing a comprehensive view of AM’s environmental footprint. Additionally, the economic dimension of sustainability is addressed through life cycle costing analysis. Production costs, energy use, and waste management are scrutinised, showcasing AM’s potential cost savings. Social life cycle assessment is introduced to assess societal impacts, focusing on worker welfare, community engagement, and overall societal well-being. A forward-looking concept of predicting sustainability before printing, using a product sustainability index, is presented. The approach emphasises environmentally responsible material selection, considering factors such as global warming potential in alloy design. This study offers a holistic approach to designing sustainable alloys and optimising AM processes through a sustainable materials science paradigm to establish the relationship amongst processing, microstructure, properties, sustainability, and performance.