Dispersion-strengthened Material Research Articles

Optimization of Dispersion-Strengthened Material Based on Copper Powder for Valve Guides of Internal Combustion Engines

The given study is dedicated to optimization of dispersion-strengthened material based on copper powder of the Cu-Al-C-O system used for valve guides of internal combustion engines. The developed material containing 3 % wt aluminum, 0.6 % wt carbon and not more than 0.02 % wt oxygen has the recrystallization temperature of 1000оС and exhibits higher tribotechnical properties comparing to the prototype. In particular, the wear out intensity of the developed material is 2.5 times lower. The material production technology is based on the method of reactionary mechanical alloying in the attritor and powder and granular metallurgy technologies.

Методика оценки остаточного ресурса лопаток турбины газотурбинного двигателя в условиях высокотемпературной ползучести

A calculation methodology for estimating the residual life of a high-pressure turbine blade based on the taking into account of the morphological state of dispersion-strengthened material is proposed. A good convergence of the calculation results with the experimental data is shown.

Evolution of microstructure and texture in a warm-rolled yttria dispersion-strengthened tungsten plate during annealing in the temperature range between 1200 °C and 1350 °C

The thermal stability of an yttria dispersion-strengthened tungsten plate warm-rolled to 50% thickness reduction is investigated. Isothermal annealing experiments were conducted at four temperatures and the microstructure and texture evolution were analyzed with Transmission Electron Microscopy (TEM) and Electron Backscatter Diffraction (EBSD) to understand the restoration mechanisms in the W-2 vol% Y2O3 alloy. At 1200 °C, dominantly recovery occurred in the warm-rolled plate up to the longest annealing time of 84 h, whereas at temperatures of 1250 °C and above recrystallization was the dominant restoration mechanism. Microstructure and texture evolution during recrystallization were quantified in terms of grain size, aspect ratio and volume fractions of fiber texture components. The analysis reveals that the Y2O3 particles play a key role in the recrystallization mechanism of the plate affecting both, nucleation and growth behavior. Their dominating effect originates from pinning of high angle boundaries causing no-convex grain shapes as well as slower recrystallization kinetics than pure tungsten, thereby improving the thermal stability of the oxide dispersion-strengthened material.

Evaluation of the Possibility of Replacement of an SCh24 Cast Iron of Detail of a “Brake Disc” of a Car by an Aluminum-Based Dispersion-Strengthened Composition Material Prepared by Internal Oxidation

This paper describes the results of the development of functional material represented by a dispersion-strengthened composition material based on aluminum and prepared by internal oxidation. Various types of tribological tests were employed; more specifically, friction tests of the specimens to determine the friction coefficient of the DSCM-brake shoe and tests of the specimens to determine wear in the DSCM-brake shoe system with subsequent use of macro- and microstructural analysis of the material of test specimens. The results of the wear of the detail made from dispersion-strengthened composition material of a “brake disc” of a car based on friction tests under dry friction depending on the composition of the composition material are given. It was stated from the results of the studies that SCh24 cast iron can be replaced by the aluminum-based dispersion-strengthened composition material.

Development of the Production Technology of Cast Aluminum Matrix Composite by Alumina Strengthening Phase Synthesis in an Aluminum Melt

Currently, critical components and assemblies made of traditional materials do not always meet the increased requirements of designers and service conditions. One solution to this problem is the development and application of dispersion-strengthened metal matrix composites. According to the informational–analytical review, a new fabrication technology of aluminum-based dispersion-strengthened composite material is presented. The peculiarities of this technology are described and sample macro- and microstructures, as well as mechanical characteristics of as-cast samples, are presented. The synthesis of strengthening particles immediately in the melt makes it possible to fabricate composites in one stage and provide thermodynamic stability, dense contact, and good adhesion between the matrix and strengthening phase. The particle sizes of the solid phase are in a range from 3 μm to 2 mm. The structural-and-phase state of the produced material is studied using optical metallography and X-ray diffraction analysis (a DRON-2 diffractometer). The microstructure is studied using a Keyence VHX-1000 microscope. The sample hardness is determined using a TKS-1M device, microhardness is determined using PMT-3 and HMV Shimadzu devices, ultimate strength is determined using ZD 10/90 and UME-10TM universal tensile testers, and impact strength is determined using an MK-30a pendulum impact tester. It is found that the variation in size and content of the strengthening phase makes it possible to vary mechanical properties of cast metal in a wide range. The application of the proposed technology will substantially decrease temporal and economical costs. A decrease in the fabrication cost of the dispersion-strengthened composite material is expected according to the results of the evaluative calculation.

Production of Highly Reinforced Dispersion-Strengthened Composite Material Based on Aluminum by Internal Oxidation

Currently dispersion-strengthened composite materials are used increasingly widely in special engineering industries. The main obstacle in the way large-scale implementation of these materials are high cost and the problem of providing a strong bond between particles and matrix under conditions of uniform particle distribution within a matrix. A method is proposed in this work for liquid-phase preparation of highly reinforced dispersion-strengthened composite material based on an aluminum alloy matrix reinforced with discrete ceramic particles. The technology developed makes it possible to reduce the cost of the dispersion-strengthened composite material obtained, in particular as a result of not using powder components and preparing composite material in a single stage. In this case a strong interphase boundary is provided between matrix and filler.

Structure and mechanical properties in a powder-processed icosahedral-phase-strengthened aluminum alloy

Nanocomposite powder particles of aluminum with dispersed icosahedral quasicrystals were produced by gas atomization from an Al-Cr-Mn-Co-Zr alloy. Bulk dispersion-strengthened material was obtained from the powder by blind-die compaction and forging. The material exhibited an attractive combination of room temperature mechanical properties with a dynamic elastic modulus of 90.5GPa, a tensile yield strength of 690MPa with 6% elongation to failure, and a high cycle fatigue life of 109cycles at 207MPa applied stress. The material also exhibited significant potential for elevated temperature applications with a modulus of 75GPa and yield strength of 400MPa at 300°C.

Low-weight TiAl3 composites by thermal explosion

Dispersion-strengthened TiAl3-based material with uniform structure and high compression strength (σc ≈ 850 MPa) was SHS-produced from Ti–Al–B4C blends in a mode of thermal explosion by using the B4C particles coated with a TiB2/TiC layer as a strengthening agent and preliminary mechanical activation of Ti–Al powder mixtures. The Ti + 3Al mixtures were mechanically activated in a planetary mill for 3 or 6 min and then 10 or 20 wt % of coated B4C particles were added. Pelleted samples were placed into a reaction chamber and heated in an electric furnace under Ar to a self-ignition temperature. The process was optimized and recommended for practical implementation.

Restoring of moldboards by abrasion-resistant dispersion-strengthened composite based on epoxy resin

A method of plough bodies’ moldboards restoring is proposed. With the view of implementation of the method a composite adhesive polymer dispersion-strengthened material based on epoxy resin is developed.

Creep-strengthening of steel at high temperatures using nano-sized carbonitride dispersions.

Creep is a time-dependent mechanism of plastic deformation, which takes place in a range of materials under low stress-that is, under stresses lower than the yield stress. Metals and alloys can be designed to withstand creep at high temperatures, usually by a process called dispersion strengthening, in which fine particles are evenly distributed throughout the matrix. For example, high-temperature creep-resistant ferritic steels achieve optimal creep strength (at 923 K) through the dispersion of yttrium oxide nanoparticles. However, the oxide particles are introduced by complicated mechanical alloying techniques and, as a result, the production of large-scale industrial components is economically unfeasible. Here we report the production of a 9 per cent Cr martensitic steel dispersed with nanometre-scale carbonitride particles using conventional processing techniques. At 923 K, our dispersion-strengthened material exhibits a time-to-rupture that is increased by two orders of magnitude relative to the current strongest creep-resistant steels. This improvement in creep resistance is attributed to a mechanism of boundary pinning by the thermally stable carbonitride precipitates. The material also demonstrates enough fracture toughness. Our results should lead to improved grades of creep-resistant steels and to the economical manufacture of large-scale steel components for high-temperature applications.

Role of Water Vapor in Chromia-Scale Growth at Low Oxygen Partial Pressure

The oxidation behavior of pure chromium and ODS-Cr alloys in Ar-H2-H2O and Ar-O2-H2O was studied at 1000°C. At high oxygen potentials, the addition of H2O to the gas had negligible effect on the scaling behavior. However, at low oxygen potentials, when the pH2O/pH2 ratio was held constant, the oxidation rate increased with water partial pressure. Increasing values of pH2O/pH2 led to more rapid rates. At fixed pH2O values, the rate increased with increasing pH2. Compact scales were formed under all conditions. In addition Cr2O3 blades grew on the scale surface when pure chromium was reacted with H2O/H2 mixtures, but not in reaction with O2/H2O. These blades did not form when Y2O3 dispersion-strengthened material was reacted. A model, in which oxide growth was sustained by diffusion of chromium vacancies and adsorption of H2O on oxide exposed to low oxygen-activity gas led to the formation of hydroxyl species, explained most of the complex effects of gas composition on scale growth and blade formation. However, it failed to account for the observed increase in scaling rate with pH2 at fixed pH2O. The latter effect is ascribed to alteration of an additional contribution to diffusion from chromium interstitials.

High-temperature deformation behavior of an Al-8.4Fe-3.6Ce dispersion-strengthened material

The high-temperature deformation behavior of a dispersion-strengthened Al-8.4Fe-3.6Ce material studied by Yaney and Nix[1] has been reanalyzed using concepts used in the analysis of the creep behavior of Al-Fe-V-Si materials. The Al-8.4Fe-3.6Ce material presents a high volume fraction of submicron dispersoids. The stress exponent and the activation energy values are anomalously high-temperature dependent, as it is usually found in most reinforced materials. Although the creep behavior of this material has been described by the deformation of dispersoids, however, direct evidence of the deformation of the second-phase precipitates was not obtained. In this work, a new approach is further developed. This approach is based on the constant substructure slip creep equation modified by the presence of an interaction between dislocations and dispersoids. This approach is able to satisfactorily predict the creep behavior of the Al-8.4Fe-3.6Ce material.

On the attractive particle–dislocation interaction in dispersion-strengthened material

The combined climb–detachment process, controlled by “interfacial pinning’ of dislocations by the attractive incoherent dispersoid particles, is critically analysed. The athermal detachment stress is recalculated (i) within the framework of the Fleischer–Friedel weak point-obstacle approximation and (ii) taking into account the particle-spacing /climb statistics. Thus inadequate restrictions of the successful model of Arzt, Rösler and Wilkinson (ARW) can be eliminated. The predicted creep thresholds cover the range from 0.13 to 0.45 (Gb/L) and are, therefore, considerably lower than the values of the ARW estimate.

Low-Cycle fatigue of dispersion-strengthened copper

The cyclic deformation behavior of a dispersion-strengthened copper alloy, GlidCop Al-15, has been studied at plastic strain amplitudes in the range 0.1 pct [<=] [Delta][var epsilon][sub p]/2 [<=] 0.8 pct. Compared to pure polycrystalline copper, the dispersion-strengthened material exhibits a relatively stable cyclic response as a consequence of the dislocation substructures inherited from prior processing and stabilized by the Al[sub 2]O[sub 3] particles. These dislocation structures remain largely unaltered during the course of deformation; hence, they do not reveal any of the features classically associated with copper tested in fatigue. At low amplitudes, the fatigue lifetimes of the dispersion-strengthened copper and the base alloy are similar; however, the former is more susceptible to cracking at stress concentrations because of its substantially greater strength. This similarity in fatigue life-times is a consequence of the dispersal of both deformation and damage accumulation by the fine grain size and dislocation/particle interactions in the GlidCop alloy. The operation of these mechanisms is reflected in the fine surface slip markings and rough fracture surface features for this material.

Hafnium carbide strengthening in a tungsten-rhenium matrix at ultrahigh temperatures

Tungsten-rhenium-hafnium carbide (W-Re-HfC) alloy is the strongest metallic material at temperatures greater than 2000 K. In the present study, the mechanical properties of tungsten and a W-3.6Re-0.26HfC alloy were determined from 1700 to 2980 K in a vacuum below 10 −5 Pa. HfC particles had an exceptional strengthening effect in the tungsten-rhenium matrix at temperatures up to 2700 K. The strengthening was attributed to the high thermodynamic stability of HfC particles at ultrahigh temperatures. The growth behavior of HfC particles in the tungsten-rhenium matrix was examined. Carbon was found to be the rate-limiting element in the growth process of HfC particles. The strengthening mechanisms in a W-3.6Re-0.26HfC were discussed. It was concluded that the strength of a dispersion-strengthened material was proportional to the square root of the volume fraction of the particles. The calculation of a W-3.6Re-0.26HfC alloy's yield strength, calculated based on the dislocation pinning and the particle statistical distribution, was in good agreement with the experimental data over the entire temperature range.

Structure refinement of Al 3Zr using lacbed technique

Nanocomposite powder particles of aluminum with dispersed icosahedral quasicrystals were produced by gas atomization from an Al-Cr-Mn-Co-Zr alloy. Bulk dispersion-strengthened material was obtained from the powder by blind-die compaction and forging. The material exhibited an attractive combination of room temperature mechanical properties with a dynamic elastic modulus of 90.5 GPa, a tensile yield strength of 690 MPa with 6% elongation to failure, and a high cycle fatigue life of 109 cycles at 207 MPa applied stress. The material also exhibited significant potential for elevated temperature applications with a modulus of 75 GPa and yield strength of 400 MPa at 300 °C.