The aim of the present research work was to investigate tribological performance and potential of Ni-based self-lubricating claddings for high temperature forming of lightweight alloys. Laser claddings included in this investigation were based on Ni-matrix with the incorporation of 5 wt% silver and 10 wt% MoS2 as solid lubricant precursors. Tribological evaluation and testing was performed by Load- Scanner to simulate hot forming process and results compared to high performance hot work tool steel. To simulate hot forming process of forging, wire drawing and extrusion, tests were done at room and elevated temperatures (150°C and 300°C) against typical light-weight alloys, including AISI 316L stainless steel, 6xxx series Al alloy and Ti6Al4V Ti alloy and results evaluated in terms of coefficient of friction vs. load, critical loads for galling initiation and volume of adhered work material. Results show that self-lubricated claddings with incorporated MoS2 and Ag as solid lubricants in general provide lower and more stable friction as well as improved galling resistance in high temperature forming of lightweight alloys. Positive effect of self-lubricating claddings intensifies with forming temperature, degree of plastic deformation and work material tendency to galling.

During forging operations, strain can occur through three primary mechanisms: strain due to load applied through dies, strain due to thermal contraction, and strain due to creep. In materials behavior models, strain due to applied load and thermal contraction are directly considered and predictions are based on thermophysical properties and flow stress behaviors as inputs to the models. Strain due to creep after forging (during cooling) is often more difficult to predict and capture due to lack of materials data. In particular, data that capture the changing flow stress behavior during cooling (rather than from isothermal testing) are not commonly available. In this project, creep strain behavior during cooling was investigated by physical simulations using a Gleeble 3500. Standard cylinder-shaped Ti-6Al-4V samples with 10 mm diameter were heated to below β-transus temperature (1775°F) or above β-transus (1925°F), followed by constant cooling rates of 250°F/min and 1000°F/min with and without applied load during cooling to 1000°F. Total strain for the tests ranged from 2 – 6%. Characterization of prior microstructure and texture was carried out using XRD, optical microscopy, and SEM. The results provide insights on the relationship of flow stress behavior and microstructure as a function of temperature and cooling rate and are applicable to forging practices. These materials data can be used as input for future process modeling, potentially giving better prediction accuracy in industry applications.

In this study, the creep properties of three titanium alloys were experimentally obtained at different applied stresses and at 683 K. X-ray diffraction and optical and electron microscopy were used to help characterize the microstructure before and after creep deformation and to show how changes in hardness correlate with the precipitation of α and ω phases in the β titanium matrix. The results of the study show that Ti-12Cr-1Fe-3Al is the most creep resistant followed by Ti-12Cr-3Al and Ti-12Cr.

This paper presents the preliminary results of experiments designed to mimic typical machining and thermal processing practices for aerospace titanium alloys. The most significant finding is that multiple side mill passes result in lower magnitude compressive stresses than a single side pass, which suggests that successive interactions with the milling tool serves to relieve residual stresses at the surface. The most likely mechanism for this is that Ti exhibits significant springback during machining, and multiple tool passes essentially remove the “springback” layer. Each successive removal of material allows stress relaxation in the remaining surface layer. By contrast, with only a single pass, surface residual stresses did not sufficiently relax.

With an aging population, war, and sports-related injuries, there is an ever-increasing demand for hard tissue replacements, such as bone. A common alloy known as Ti- 6Al-4V is used in such tissue replacement and is well-tolerated in in-vivo conditions. Recently, however, there has been great concern on the dissolution of aluminum and vanadium ions into the body fluid and the possibility of a toxic result, which is caused by poor integration with the human environment. Without the ability to attach and surround the biomaterials with osteoblast cells, the surrounding tissue will recede from material, release ions or debris, and thereby require immediate revision surgery. In order to reduce this effect it is necessary to nullify factors that can be linked with poor osseo-integration. Laser surface processing creates a physical texture on Ti-6Al- 4V alloys and has been hypothesized to improve bone integration and tissue growth on metallic implants. This form of engineering will be used in this study whose goal is to find the optimal laser processing parameters, based upon laser fluence values, to improve Ti-6Al-4V alloys biocompatibility. Contact angle, surface energy, and roughness measurements were taken. Through response surface analysis, the optimal parameter of 2250W by 1000mm/s was concluded.

Ti-6Al-4V alloy is characterized to be sensitive to heat treatment and deformation. This paper focuses on microstructural evolution and variation in mechanical properties with respect to the deformation and change in the heat treatment cycle. Different heat treatment cycles such as mill annealing, solution treatment and beta solution treatment followed by annealing were carried out on deformed and undeformed Ti-6Al-4V samples. Heat treated samples were studied using optical and scanning electron microscopy. Also different mechanical tests (i.e. tensile test, fracture toughness test) were conducted and results were analyzed. Large variation in mechanical properties and microstructures were found out with different heat treatment cycles. Fracture toughness was found to be high for beta solution treatment samples than the mill annealed and solution treated samples and the reason for the same has been analyzed.

This paper presents the results of an experimental investigation of the effect of three types of post-heat treatments: 1) solution treatment and aging, 2) stress relieving, and 3) annealing on the corrosion behavior of Ti-6Al-4V fabricated via direct metal laser sintering (DMLS). The microstructure and phase evolution as affected by heat treatment temperature were examined through scanning electron microscopy and via x-ray diffraction. The Vicker’s microhardness, as it was affected by various heat treatments, was compared. The corrosion behavior of the specimens was measured electrochemically in simulated body fluid at 37°C. It was found that the nonequilibrium α’ phase with a small amount of β nuclei was formed in the as-fabricated sample. Heat treatments allow the formation of the β phase and the agglomeration of β precipitates to occur at elevated temperatures. Transformed β phase with various morphologies was observed as a result of the heat treatments. Different degrees of improvement in the corrosion resistance were observed in the solution-treated and aged samples, 650 °C stress relieved, and annealed samples.

Aeronautical engineers are consistently searching for new and optimal materials to achieve specific applications throughout an airframe. There are a multitude of considerations affecting the structural design of an aircraft such as the complexity of the load distribution through a redundant structure, the large number of intricate systems required in an airplane and the operating environment of that airframe. All of the above criteria is governed primarily by weight savings. Thus, the optimal materials selected today and for the future of airframes are composite material and titanium.