High temperature deformation processing maps for boron modified Ti-6Al-4V alloys

The alloy, Ti-6Al-4V is an alpha + beta Ti alloy that has large prior beta grain size (similar to 2 mm) in the as cast state. Minor addition of B (about 0.1 wt.%) to it refines the grain size significantly as well as produces in-situ TiB needles. The role played by these microstructural modifications on high temperature deformation processing maps of B-modified Ti64 alloys is examined in this paper.Power dissipation efficiency and instability maps have been generated within the temperature range of 750-1000 degrees C and strain rate range of 10(-3)-10(+1) s(-1). Various deformation mechanisms, which operate in different temperature-strain rate regimes, were identified with the aid of the maps and complementary microstructural analysis of the deformed specimens. Results indicate four distinct deformation domains within the range of experimental conditions examined, with the combination of 900-1000 degrees C and 10(-3)-10(-2) s(-1) being the optimum for hot working. In that zone, dynamic globularization of alpha laths is the principle deformation mechanism. The marked reduction in the prior beta grain size, achieved with the addition of B, does not appear to alter this domain markedly. The other domains, with negative values of instability parameter, show undesirable microstructural features such as extensive kinking/bending of alpha laths and breaking of beta laths for Ti64-0.0B as well as generation of voids and cracks in the matrix and TiB needles in the B-modified alloys. (C) 2010 Elsevier B.V. All rights reserved

A simple and versatile machine for creep testing at low loads (6-300 N) and on miniaturized specimens: Application to a Mg-base alloy

High temperature creep testing at a very lowload range (< 10 N) on miniaturized specimens has always been a challenge due to inherent design limitation (such as significant preload) of the conventional creep testing machines. In the present study, the challenge was overcome by developing a simple and versatile horizontal creep testing machine to conduct creep tests in the loading range of similar to 6-300 N in tension and in compression. The competence of the in-house-built horizontal creep machine was validated by conducting creep testing on dog-bone shaped sheet specimens of cast Mg-1Sn-1Ca (TX11) Mg-base alloy over a lower stress range of 1.6-5.9 MPa (equivalent load range of 6.4-18.1 N) at 450 degrees C and in the high stress range of 20-80 MPa (equivalent load range of 76-310 N) at 175 degrees C. Published by AIP Publishing

A simple and versatile machine for creep testing at low loads (6–300 N) and on miniaturized specimens: Application to a Mg-base alloy

High temperature creep testing at a very low load range (<10 N) on miniaturized specimens has always been a challenge due to inherent design limitation (such as significant preload) of the conventional creep testing machines. In the present study, the challenge was overcome by developing a simple and versatile horizontal creep testing machine to conduct creep tests in the loading range of ∼6–300 N in tension and in compression. The competence of the in-house-built horizontal creep machine was validated by conducting creep testing on dog-bone shaped sheet specimens of cast Mg-1Sn-1Ca (TX11) Mg-base alloy over a lower stress range of 1.6–5.9 MPa (equivalent load range of 6.4–18.1 N) at 450 °C and in the high stress range of 20–80 MPa (equivalent load range of 76–310 N) at 175 °C

On Joule heating during spark plasma sintering of metal powders

Joule heating as a primary heating source mechanism was probed during Spark Plasma Sintering (SPS) of pure metal powders (Fe, Ni and Cu). Resistance to electric path was estimated from voltage–current measurements obtained online during these experiments. Resistance was observed to saturate at the same value irrespective of the type of metal powder, after attaining a sintering temperature of &#8764;0.3T_m. This saturation in resistance is attributed primarily to the Joule heating that occurs at the graphite-foil and punch in an SPS system

Plasma-sprayed high entropy alloys: microstructure and properties of AlCoCrFeNi and MnCoCrFeNi

High Entropy Alloys (HEAs) represent a new class of materials that present novel phase structures and properties. Apart from bulk material consolidation methods such as casting and sintering, HEAs can also be deposited as a surface coating. In this work, thermal sprayed HEA coatings are investigated that may be used as an alternative bond coat material for a thermal barrier coating system. Nanostructured HEAs that were based on AlCoCrFeNi and MnCoCrFeNi were prepared by ball milling and then plasma sprayed. Splat studies were assessed to optimise the appropriate thermal spray parameters and spray deposits were prepared. After mechanical alloying, aluminum-based and manganese-based HEA powders revealed contrary prominences of BCC and FCC phases in their X-ray diffraction patterns. However, FCC phase was observed as the major phase present in both of the plasma-sprayed AlCoCrFeNi and MnCoCrFeNi coatings. There were also minor oxide peaks detected, which can be attributed to the high temperature processing. The measured porosity levels for AlCoCrFeNi and MnCoCrFeNi coatings were 9.5 &#177; 2.3 and 7.4 &#177; 1.3 pct, respectively. Three distinct phase contrasts, dark gray, light gray and white, were observed in the SEM images, with the white regions corresponding to retained multicomponent HEAs. The Vickers hardness (HV0.3kgf) was 4.13 &#177; 0.43 and 4.42 &#177; 0.60 GPa for AlCoCrFeNi and MnCoCrFeNi, respectively. Both type of HEAs coatings exhibited anisotropic mechanical behavior due to their lamellar, composite-type microstructure

Comparison of plasma sprayed High Entropy Alloys with conventional bond coat materials

High Entropy Alloys (HEAs) are a new class of alloys with multi-principle elements in an equi-atomic ratio that present novel phase structures. HEAs are known for their high temperature microstructural stability, enhanced oxidation and wear resistance properties. Apart from bulk material consolidation methods such as casting and sintering, HEAs can also be deposited as a surface coating. In this work, thermal sprayed HEA coatings are investigated as an alternative bond coat material for a thermal barrier coating system. Nanostructured HEAs that were based on AlCoCrFeNi and MnCoCrFeNi were prepared by ball milling and then plasma sprayed. Splat studies were assessed to optimize the appropriate thermal spray parameters and spray deposits were prepared. Subsequently, the microstructure and mechanical properties of two HEAs coatings of different composition were characterized and compared to conventional plasma spray NiCrAlY bond coats