One of the methods of evaluating the mechanical properties of a material in the case of its limited amount is the use of techniques that employ the miniaturized test specimens. The basic properties used mostly for residual life evaluation are tensile strength, impact notch toughness or impact notch toughness transition curve, fracture toughness, creep and high cycle fatigue. For example, by semi-destructive sampling of operating power equipment, actual material properties can be obtained which are crucial for predicting the residual life of the equipment. Furthermore, the local material properties of the weld joint in individual zones can be determined. In this paper applicability of these test methods is described, specific examples of use are given and reference is made to the existing ISO/ASTM 52909:2022 standard for the use of sub-size samples.

IN718 has good fabricability, high strength at elevated temperature, and corrosion resistance, and it is widely deployed in many aerospace and other high-performance applications. With the molten pool rapid solidification during laser powder bed fusion (L-PBF), the resulting microstructure is anisotropic and inhibits macro-segregation. The as-built condition usually exhibits lower mechanical properties. Four different heat treatment procedures were designed and tested to study the effect of different heat treatment parameters on the type of precipitates and grain size. The investigated heat treatment procedures showed the formation of equiaxed grain size and a significant amount of γ' and γ" particles at the grain boundary in addition to primary carbide types (MC). Three types of microstructure characteristics and grain size were achieved. Coarse grain size suitable for creep application was achieved by increasing the soaking time at the aging cycle. The formation of serrated grain boundaries suitable for good fatigue and creep properties was achieved by decreasing the stress relief cycle's soaking time and temperature. Fine-grain size, which is preferable for fatigue properties, was achieved by decreasing the soaking time at the solution annealing cycle.

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.

The microstructure of 25Cr-35Ni-0.4C refractory steels consists of an austenitic matrix and eutectic carbides precipitated in the interdendritic regions. In-depth studies of the morphology and chemical composition of these carbides are extremely important for industry, since the microstructural components of these steels are responsible for their hot mechanical properties. In this context, the microstructural characterization of ASTM A297 Grade HP 40 steels modified with niobium and zirconium is using scanning electron microscopy, microanalysis and X-ray diffraction, and determination of the time to rupture at 1100ºC under a constant stress of 17 MPa is reported here.