Mechanical Properties of Laser-Deposited Ti-6Al-4V

Laser additive manufacturing is a solid-freeform-fabrication process which is being investigated for titanium-component manufacturing and repair based on its cost-reduction potential and flexibility. Laser additive manufacturing also has the potential to improve mechanical properties due to the high cooling rates involved. However, the effect of the layered manufacturing process and any lack-of-fusion porosity and texture on the magnitude and anisotropy of mechanical properties is of concern. Hence, a preliminary effort was undertaken to assess these effects for bulk Ti-6Al-4V deposits manufactured using the LENS™ process. Tension, fatigue, and crack-growth tests were performed on both stress-relieved and HIP’ed deposits in three primary directions. The results were compared to published data for conventionally processed Ti-6Al-4V castings and forgings.Mechanical Engineerin

Magnetic and vibrational properties of high-entropy alloys

The magnetic properties of high-entropy alloys based on equimolar FeCoCrNi were investigated using vibrating sample magnetometry to determine their usefulness in high-temperature magnetic applications. Nuclear resonant inelastic x-ray scattering measurements were performed to evaluate the vibrational entropy of the ^(57)Fe atoms and to infer chemical order. The configurational and vibrational entropy of alloying are discussed as they apply to these high-entropy alloys

The Effect of Hot Deformation Parameters on Microstructure Evolution of the α-Phase in Ti-6Al-4V

The effect of high-temperature deformation and the influence of hot working parameters on microstructure evolution during isothermal hot forging of Ti-6Al-4V in the alpha phase field were investigated. A series of hot isothermal axis-symmetric compression tests were carried out at temperatures both low and high in the alpha stability field [(1153 K and 1223 K (880 °C and 950 °C), respectively], using three strain rates (0.01, 0.1 and 1.0/s) relevant to industrial press forging. The microstructures and orientation of the alpha laths were determined using optical microscopy and electron backscatter diffraction techniques. The experimental results show that there is a change in lath morphology of the secondary α phase under the influence of the deformation parameters, and that α lath thickness appears to have little influence on flow behavior

Features of Duplex Microstructural Evolution and Mechanical Behavior in the Titanium Alloy Processed by Equal‐Channel Angular Pressing.

This report describes a study of the regularities in the kinetics of microstructure evolution and recrystallization processes in the Ti–5.7Al–3.8Mo–1.2Zr–1.3Sn alloy (Russian analogue VT8M‐1) during processing by equal‐channel angular pressing (ECAP). To produce a duplex (globular‐lamellar) structure, the billets are subjected to preliminary heat treatment, including water‐quenching from a temperature below the β‐transus followed by annealing at 700 °С. For the ECAP temperature selection, the deformation behavior of the alloy with a duplex structure is investigated under upsetting in the temperature range of 650–800 °С. The evolution of the globular and lamellar fractions is examined during ECAP processing, and an emphasis is placed on the role of phase transformations, dynamic recrystallization, and spheroidization of the α‐phase which is realized with increasing accumulated strain when processing by ECAP. It is demonstrated that after 6 ECAP passes an equiaxed ultrafine‐grained structure is formed with a mean α‐phase grain/subgrain size of ≈0.6 μm. The investigation includes an examination of the effect of microstructure on the mechanical properties of the alloy

A two-step approach for producing an ultrafine-grain structure in Cu-30Zn brass

A two-step approach involving cryogenic rolling and subsequent recrystallization annealing was developed to produce an ultrafine-grain structure in Cu-30Zn brass. The material so processed was characterized by a mean grain size of 0.5 μm, fraction of high-angle boundaries of 90 pct., a weak crystallographic texture, and strength twice that of initial material

Annealing behavior of cryogenically-rolled Cu-30Zn brass

The static-annealing behavior of cryogenically-rolled Cu-30Zn brass over a wide range of temperature (100-900 °C) was established. Between 300 and 400 °C, microstructure and texture evolution were dominated by discontinuous recrystallization. At temperatures of 500 °C and higher, annealing was interpreted in terms of normal grain growth. The recrystallized microstructure developed at 400 °C was ultrafine with a mean grain size of 0.8 μm, fraction of high-angle boundaries of 90 pct., and a weak crystallographic texture

Absence of long-range chemical ordering in equimolar FeCoCrNi

Equimolar FeCoCrNi alloys have been the topic of recent research as "high-entropy alloys," where the name is derived from the high configurational entropy of mixing for a random solid solution. Despite their name, no systematic study of ordering in this alloy system has been performed to date. Here, we present results from anomalous x-ray scattering and neutron scattering on quenched and annealed samples. An alloy of FeNi_3 was prepared in the same manner to act as a control. Evidence of long-range chemical ordering is clearly observed in the annealed FeNi_3 sample from both experimental techniques. The FeCoCrNi sample given the same heat treatment lacks long-range chemical order

Effect of electric-current pulses on grain-structure evolution in cryogenically rolled copper

The effect of electric-current pulses on the evolution of microstructure and texture in cryogenically rolled copper was determined. The pulsed material was found to be completely recrystallized, and the recrystallization mechanism was deduced to be similar to that operating during conventional static annealing. The microstructural changes were explained simply in terms of Joule heating. A significant portion of the recrystallization process was concluded to have occurred after pulsing; i.e., during cooling to ambient temperature. The grain structure and microhardness were shown to vary noticeably in the heat-affected zone (HAZ); these observations mirrored variations of temper colors. Accordingly, the revealed microstructure heterogeneity was attributed to the inhomogeneous temperature distribution developed during pulsing. In the central part of the HAZ, the mean grain size increased with current density and this effect was associated with the temperature rise per se. This grain size was slightly smaller than that in statically recrystallized specimens

Normalised model-based processing diagrams for additive layer manufacture of engineering alloys

Additive Layer Manufacturing (ALM) is becoming a more widely accepted method for the production of near net-shape products across a range of industries and alloys. Depending on the end application, a level of process substantiation is required for new parts or alloys. Prior knowledge of the likely process parameter ranges that will provide a target region for the process integrity can save valuable time and resource during initial ALM trials. In this paper, the parameters used during the powder bed ALM process have been taken from the literature and the present study to construct normalised process maps for the ALM process by building on an approach taken by Ion et al. in the early 1990's (J.C. Ion, H.R. Shercliff, M.F. Ashby, Acta Metallurgica et Materialia 40 (1992) 1539e1551). These process maps present isopleths of normalised equivalent energy density (E0*) and are designed to provide a practical framework for comparing a range of ALM platforms, alloys and process parameters and provide a priori information on microstructure. The diagrams provide a useful reference and methodology to aid in the selection of appropriate processing parameters during the early development stages. This paper also applies the methodology to worked examples of Tie6Ale4V depositions processed using different Electron Beam Melting parameters