Materials Science Forum Vol. 1146

Abstract: This investigation focuses on the microstructural refinement of the γ-TiAl intermetallic alloy Ti-45Al-2Nb-2Mn (at.%) + 0.8 (vol.%) TiB2 (Ti4522XD) processed by powder metallurgy. The alloy powders were manufactured using the Electrode Induction-melting Gas Atomization (EIGA) process and subsequently consolidated through Hot Isostatic Pressing (HIP), resulting in a near-γ microstructure.The study further explores the effects of three distinct thermal treatments on the microstruc ture: 1) heating to 1300°C for 2 hours followed by furnace cooling (HT1), 2) heating to 1300°C for 2 hours, then water quenching and aging at 850°C for 8 hours before furnace cooling (HT2), and 3) heating to 1300°C for 2 hours, followed by water quenching and aging at 700°C for 8 hours before furnace cooling (HT3). These processes were tailored to promote the development of duplex (DP) and fully lamellar (FL) microstructures. Characterization was performed using X-ray diffraction (XRD) to identify phase distributions and scanning electron microscopy (SEM) to examine the surface morphology. Transmission elec tron microscopy (TEM) was used for a preliminary assessment of actual lamellar spacing. As a result, two different microstructures were obtained: DP for HT1 and near fully lamellar (NFL) for HT2 and HT3, but differences in the final actual lamellar spacing were observed for these last two cases. Additionally, the presence of microcracks of different morphologies was observed by SEM prior to any mechanical testing.

Abstract: Co additions to titanium aluminides were assessed to decrease the typically high sintering temperatures necessary for the densification of intermetallics. Compositions based on the binary Ti-45Al with ternary Co variations between 1-10 at.% were investigated. The specimens were cylinders with 8 mm diameter prepared using blended elemental powders followed by cold uniaxial pressing. Sintering was carried out under an argon atmosphere at different temperatures ranging from 1100 to 1400 °C for 2 hours in a tube furnace. The results indicated that there was a systematic increase in densification with Co additions. The relative density of the reference material Ti-45Al was approximately 53%, however, Co addition of 10% led to densifications in the order of 80%. A strong effect of decreasing the sintering temperature was achieved with Co additions. The microstructure changed from fully lamellar with 1 at.% Co sintered at 1400 °C to duplex with higher Co additions sintered at 1200 °C. Besides the γ-TiAl and α₂-Ti₃Al equilibrium phases, the formation of a CoAl₂Ti intermetallic was identified. The addition of 7% Co led to the highest hardness of approximately 450 HV.

Abstract: TiAl alloy is a high-temperature structural material that is highly sensitive to microstructure. Different hot working or heat treatment processes can refine the grain, release stress, and adjust the phase type and distribution. This study investigates the effect of heat treatment and rolling on the microstructure of powder metallurgy TiAl alloys in detail, resulting in TiAl alloys with high plasticity achieved through hot pack rolling. The heat treatment temperature was set between 1290°C and 1330°C, with a temperature interval of 10°C, a holding time of 30 minutes, and cooling with the furnace. Spheroidization of the grains occurred at 1310°C. Phase analysis of the TiAl alloy was conducted after heat treatment at 1290°C, 1310°C, and 1330°C. The microstructure of the TiAl alloy after heat treatment at 1290°C still consisted of γ phase and B2 phase, with no significant change in the content of γ phase and B2 phase. After heat treatment at 1310°C, numerous α₂ phases abruptly emerged in the microstructure. The TiAl sheet exhibits an elongation of 3.6% at room temperature, which increases to 65% at 700°C. The study investigated the phase transformation process, grain morphology, and microstructure evolution of powder metallurgy TiAl alloy under different heat treatment temperatures and rolling. The relationship between microstructure and temperature of powder metallurgy TiAl alloy was established using electron backscattering diffraction.

Abstract: Titanium matrix composites (TMCs) have found extensive application in aerospace, biomedical, and military sectors due to their exceptional strength-to-weight ratio and wear resistance at ambient and elevated temperatures. Nevertheless, conventional production methods often face a compromise between cost and performance, thus limiting the suitability of this material for broad utilization in engineering contexts. Recent research findings indicate that the utilization of manufacturing techniques such as hydrogen assisted blended elemental powder metallurgy (HABEPM) with the incorporation of a double press-and-sinter option, as well as the sintering of powder blends that have been preliminarily activated through milling, can both serve as economically viable methods for the production of highly dense TMCs with satisfactory mechanical properties. Both methods guarantee the activation of sintering in powders, resulting in notable improvements in density and a more refined and uniform microstructure compared to porous and nonuniform composites obtained through traditional vacuum sintering of powder blends. This study provides novel insights into the design and production of cost-effective and environmentally friendly TMCs with determined mechanical properties.

Abstract: TiBw reinforced titanium matrix composites (TMCs) are the most promising engineering materials in aerospace and transportation owing to their excellent properties such as lightweight, high strength, wear resistance. The electron beam powder bed fusion (EB-PBF) characterized by its rapid solidification process during the manufacturing, which can effectively controlling the microstructure and mechanical properties of DRTMCs. The state of feedstock used in EB-PBF has a significant influence on the microstructure and mechanical properties of DRTMCs prepared by EB-PBF. However, there is no commercial feedstock available for EB-PBF fabricating DRTMCs. The disadvantages of premixed ball-milled powder are degraded flowability or incomplete reaction and agglomeration of reinforcements, which causes metallurgical defects in the as-fabricated composites. These issues severely affect the stability of mechanical properties of DRTMCs prepared by EB-PBF. The introduction of TiBw led to the formation of melt pool structure. At the boundary of the melt pool, TiBw exhibits an equiaxed continuous network distribution, while at the center of the melt pool, TiBw exhibits a columnar continuous network distribution; Moreover, the introduction of TiBw resulted in a 75% grain refinement, a 40% increase in yield strength, a 54% increase in tensile strength, and a decrease in elongation (13.2%) in the composite material. The improvement in strength of Ti-TiBw composite material prepared by EBM is due to grain refinement and the good load transfer effect generated by high aspect ratio TiBw, while the decrease in plasticity of the composite material is due to the connectivity failure of TiBw on the matrix. Based on the current research of DRTMCs prepared by EB-PBF, the future research trend focus on TiBw reinforced DRTMCs prepared by EB-PBF is discussed.

Abstract: Additive Manufacturing technologies revolutionize the production of 3D components by selectively depositing material layers, facilitating intricate geometries and cavities with minimal material waste. Among these techniques, Plasma Metal Deposition (PMD) stands out as a powder-based method offering promising applications, particularly in the aerospace sector.In this study, five specimens manufactured via PMD have been investigated, employing a base material of Grade 2 titanium and a welding material comprising a powder blend of grade 1 titanium and 30% B₄C particles. The incorporation of boron carbide aims to further augment the already commendable properties of titanium, catering to the stringent requirements of the aerospace industry.Attention is directed towards key manufacturing parameters such as the transferred arc and torch travel speed, while maintaining fixed parameters including pilot arc, current, and torch-substrate height. The primary objective of this research is to comprehensively explore the PMD technique, scrutinizing potential thermodynamic reactions during the welding process between titanium and boron carbide. Concurrently, thorough characterization of the specimens will be conducted to elucidate their properties.This project seeks to optimize the PMD manufacturing process and enhance the performance characteristics of the produced parts, thereby addressing critical needs in the aerospace sector. By unravelling the intricacies of thermodynamic interactions and material properties, we aim to pave the way for advancements in additive manufacturing methodologies and the production of high-performance titanium components for aerospace applications

Abstract: Metal matrix composites (MMCs) have received considerable attention due to their low density with good elastic modulus and high strength to weight ratio. Discontinuous reinforced Ti matrix composites have been found as a promising material for applications in various fields, such as aerospace, automotive, biomedical and advanced military applications, because of their low cost, improved performance and ease of fabrication. Among the discontinuous ceramic reinforcements, TiC is identified as a very suitable reinforcement for the Ti system because of its excellent properties and high compatibility with Ti matrices. In this study, investigations have been conducted on the influence of volumetric percentage of TiC (10%) on microstructural development of TiC reinforced titanium beta matrix composite prepared by the blended elemental method from hydrided powders using ex situ processing route. Samples were produced by mixing of elemental hydrided powders followed by uniaxial and cold isostatic pressing with subsequent densification by sintering (900°C- 1500°C), in high vacuum. Sintered samples were characterized for phase composition, microstructure, microhardness and mechanical properties by X-ray diffraction, scanning electron microscopy, Vickers indentation, respectively. Density was measured by Archimedes method. The experiment results revealed that TiC content has significant influence on the microstructure and improving the hardness values of Ti-35Nb-TiC composites. A homogeneous distribution of TiC particles was observed, with a reduced presence of agglomerates and macroporosities. There was an increase of 28.5 % in the hardness of the composites with the addiction of TiC, which indicates the possibility of using components manufactured using this technique, for example, in aircraft landing gears that are subject to high mechanical stress and orthopedic implants.

Abstract: In the aerospace industry, titanium and its alloys have garnered significant attention for their low density, rendering them highly desirable materials. Nonetheless, their wear resistance has posed challenges, prompting extensive research into titanium-based composite materials. This study investigates the tribological performance of various titanium-based metal specimens reinforced with distinct ceramic and intermetallic materials. Specifically, specimens were fabricated to include a 20% volume fraction of pre-alloyed TiAl intermetallics, renowned for their reduced density, while others incorporated 30% boron carbide (B₄C). All specimens were meticulously prepared using Inductive Hot Pressing under optimized conditions. The primary objective is to discern the most effective option in terms of wear resistance. Comprehensive analyses, encompassing mass loss measurements, track width evaluations, wear assessments, and friction coefficient analyses, were conducted to achieve this goal.

Abstract: Titanium alloys are widely used in aerospace applications due to their excellent strength-to-weight ratio, corrosion resistance, and high temperature performance. However, including nanoparticles as reinforcement in titanium alloys can further improve their mechanical properties, making them even more suitable for demanding aerospace applications. Titanium matrix composites (TMC) are titanium alloys typically reinforced with micron-sized ceramic particles. These reinforcements improve some properties, such as strength, but deteriorate others. However, reducing the size of reinforcements to the nanometer range allows for larger reinforcement effects to be obtained with much smaller volumetric fractions of reinforcement, which is less detrimental to fatigue, toughness, ductility, etc. This work focuses on the study of simple and safe manufacturing routes for nanoreinforced Ti alloys that increase the strength of the base material with a low negative effect on ductility. The selection of the compositions and treatment temperatures was carried out using binary phase diagrams and experimental results.