Study of Ti – Al based high-temperature cermet filters

Operation in corrosive media and/or at high temperatures requires improved characteristics of the performance and durability of filtering equipment. The Ti – Al intermetallic system combines low density with high strength and exhibits high resistance to oxidation and corrosion at elevated temperatures. We present the results of studying high-temperature Ti – Al cermet products (filters) with nanoscale pores. Filters were obtained from a mixture of Ti and Al powders (mass ratio 40:60) by thermal explosion. XRD methods showed that the synthesized material consists of two main phases: TiAl3 and Al2O3. The microstructure analysis revealed the presence of large-sized TiAl3 structures and spherical Al2O3 aggregates enveloped by nanostructured TiAl3. Moreover, nanoscale fibrous TiAl3 compounds forming a multilevel developed cobweb-like structure are observed in the entire volume of the pore space of the material. The open porosity of the material was 48%, the pore size was 0.1 – 0.2 μm, the efficiency of the porous material was 99.999%, the resistance to gas flow was 100 mm of water column, and the filtration index was 0.062. Thermal tests revealed the possibility of effective use of filters under conditions of elevated (up to 800°C) temperatures and corrosive media due to the chemically stable and heat-resistant binary structure of the material. The results obtained can be used to improve the methodology of the development and operation of high-temperature cermet filters based on Ti – Al.

Deformation Twinning in a Metal-Intermetallic System: Novel Paradigm for Designing Alloys with Exceptional Strength-Ductility Combination

Engineering applications of high strength alloys are often restricted due to their poor tensile elongation or ductility. Alloys with high yield strength typically exhibit limited strain-hardenability (the difference between tensile and yield-strengths), leading to reduced tensile ductility. Deformation twinning, resulting in high strain hardenability, can lead to enhanced tensile elongation in single-phase solid solutions, including high entropy alloys (HEAs). However, alloy systems involving a solid solution matrix strengthened with an intermetallic phase do not exhibit deformation twinning, thus limiting their tensile ductility. We have successfully exploited deformation twinning in a novel HEA, strengthened using nano-lamellar ordered multi-component intermetallic precipitates, leading to an exceptionally high yield strength (~1630 MPa), good tensile ductility (~15%), and ultimate tensile strength (~1720 MPa), higher than any other reported fcc based alloy. Exploiting deformation twinning in a two-phase metal-intermetallic system, offers a new paradigm for addressing the strength-ductility trade-off plaguing alloy design.

Producing of Tix-Aly Intermetallic Coatings on the Surface of Pre-Nitriding Punching Tools

The problem of punching tools resistance increasing is investigated. Methods for intermetallic coatings synthesis are investigated. Mathematical model of vacuum ion-plasma deposition process allowing predicting coatings composition basing on intermetallic system Ti-Al was developed. Experimental verification confirmed the adequacy of the computer model. The technology hardening punching tools with wear-resistant coatings deposition based on intermetallic Ti-Al system on pre-nitriding surface in vacuum was developed. Production tests of the hardened punching tools were carried out.

Processing of CuZr Based Shape Memory Alloys

In the present work an investigation on primary processing of CuZr based shape memory alloys is proposed. In particular, the study addresses the effect of hot rolling process on the properties of CuZr shape memory alloys, in which the addition of some elements, such as Cr, Co and Ni, is taken into account. These alloys are produced by means of vacuum arc melting furnace under non contaminating conditions. Considering the high reactivity of these alloys, due to Zr element, hot working was undertaken after sealing the ingot cigars in a stainless steel protective can. The characterization of the rolled alloys is performed using DSC in terms of evolution of martensitic transfor-mation temperatures. The analysis is completed with mechanical and the microstructure investigations by means of microhardness and scanning electron microscopy (SEM) observations, respectively. The main result of this work is the evaluation of hot workability property of this system, which can be improved by adding metallic elements to the binary CuZr intermetallic system. Moreover, interesting characteristics, such as high transformation temperatures, thermal stability and reduced thermal hysteresis, can be also improved by means of the addition of Ni and Co at the same time.