Microstructural, microhardness and electrochemical properties of heat-treated LENS in-situ synthesized Ti-Al-x(Mo, Si) alloys.

So as to explore the opportunity of property enhancement of TiAl-based alloys, studies of microstructural evolution after processing with heat treatments are to be expected. Therefore, the objective of this present study is to investigate how additions of silicon (Si) and molybdenum (Mo) as alloying elements affects the microstructure, microhardness, corrosion behaviour, and wear properties of Ti-Al-x(Mo, Si) alloys made from constituent elemental powders through in-situ alloying laser engineered net shaping (LENS) technique. The influence of the feed rate of Si powder (0.1 rpm, 0.2 rpm and 0.3 rpm) on Ti-Al-xMo was studied at 0.1 rpm and 0.2 rpm Mo feed rate, respectively. Heat treatment at 1200 °C for 15, 30, and 60 min was performed after LENS in-situ alloying, and furnace cooling (FC) was the final step. The microstructure of the produced alloys was analyzed via Scanning electron microscopy (SEM) fitted with energy dispersive spectroscopy (EDS). Using a tribometer and a potentiodynamic polarization test, the alloys' wear characteristics and corrosion behaviour were studied. Based on the results, it was noticed that microhardness values decrease after heat treatment for all the samples produced. Owing to the combined effects of Mo and Si, both the ßo-TiAl and ζ-Ti5Si3 phases lead to solid precipitation hardening and solution strengthening at the grain boundaries. The XRD analysis confirmed γ, α2, α, ßo and ζ-Ti5Si3 phases occurrence in the as-built alloys. The LENS fabricated alloys demonstrated improved wear properties and marginally change in corrosion behavior after heat treatment.

Ceramic Matrix Composites Obtained by the Reactive Sintering of Boron Carbide with Intermetallic Compounds from the Ti-Si System.

In this study, we investigated the effect of adding two different intermetallics, Ti5Si3 and TiSi2, for the preparation of TiB2-SiC-B4C composites. As part of the research, stoichiometric composites consisting only of two phases TiB2 and SiC were obtained. The TiB2-SiC-B4C composites were prepared via pressureless sintering. The presence of the phases in the sintered composites was confirmed using X-ray diffraction and scanning electron microscopy. The SEM-EDS examination revealed that the TiB2 and SiC phases were formed during the composite process synthesis and were distributed homogeneously in the B4C matrix. The obtained results allowed us to usually exceed 2000 °C and the use of specialized equipment for firing, that is, vacuum or protective atmosphere furnaces as well as control and measurement equipment. Such an approach generates high costs that are decisive for the economics of the technological processes. In the case of our compositions, it is possible to lower the temperature to 1650 °C. The TiB2-SiC-B4C composites were classified as UHTCs.

Microstructure and Properties of TiB2 Composites Produced by Spark Plasma Sintering with the Addition of Ti5Si3.

Titanium diboride (TiB2) is a hard, refractory material, attractive for a number of applications, including wear-resistant machine parts and tools, but it is difficult to densify. The spark plasma sintering (SPS) method allows producing TiB2-based composites of high density with different sintering aids, among them titanium silicides. In this paper, Ti5Si3 is used as a sintering aid for the sintering of TiB2/10 wt % Ti5Si3 and TiB2/20 wt % Ti5Si3 composites at 1600 °C and 1700 °C for 10 min. The phase composition of the initial powders and produced composites was analyzed by the X-ray diffraction method using CuKα radiation. The microstructure was examined using scanning electron microscopy, accompanied by energy-dispersive spectroscopy (EDS). The hardness was determined using a diamond indenter of Vickers geometry loaded at 9.81 N. Friction-wear properties were tested in the dry sliding test in a ball-on-disc configuration, using WC as a counterpart material. The major phases present in the TiB2/Ti5Si3 composites were TiB2 and Ti5Si3. Traces of TiC were also identified. The hardness of the TiB2/Ti5Si3 composites was in the range of 1860-2056 HV1 and decreased with Ti5Si3 content, as well as the specific wear rate Wv. The coefficient of friction for the composites was in the range of 0.5-0.54, almost the same as for TiB2 sinters. The main mechanism of wear was abrasive.

Microstructural Characterization of Melt Extracted High-Nb-Containing TiAl-Based Fiber.

The microstructure of melt extracted Ti-44Al-8Nb-0.2W-0.2B-1.5Si fiber were investigated. When the rotation speed increased from 2000 to 2600 r/min, the appearance of the wire was uniform with no Rayleigh-wave default. The structure was mainly composed of fine α2 (α) phase dendritic crystal and a second phase between dendrite arms and grain boundaries. The precipitated second phases were confirmed to be Ti5Si3 from the eutectic reaction L→Ti5Si3 + α and TiB. As the lower content of Si and higher cooling rate, a divorced eutectic microstructure was obtained. Segregation of Ti, Nb, B, Si, and Al occurred during rapid solidification.