Influence Of Thermomechanical Processing Research Articles

On the Influence of Thermomechanical Processing on the Fracture Behavior of Gamma-Based Titanium Aluminides. II. Effects of Alloying with Cr and Nb

ABSTRACT The effects of microstructure on the tensile and fracture behavior of Ti-48Al-1.5Cr and Ti-48Al-2Cr-2Nb (compositions stated in atomic % unless stated otherwise) are investigated. Microstructures with different equiaxed/lamellar grain size and volume fractions are produced by extrusion with reduction ratios of 10:1 and 14:1, prior to annealing in the α + γ and/or α + γ phase fields. Room-and elevated-temperature tensile ductility, yield strength and ultimate tensile strength are shown to exhibit an inverse square root dependence on the average equiaxed/lamellar grain size in Ti-48Al-1.5Cr extruded with a 14:1 reduction ratio. A similar Hall-Fetch dependence of room-temperature fracture toughness on the average equiaxed/lamellar grain size is also demonstrated in the Ti-48Al-I.5 Cr alloy extruded with a reduction ratio of 14:1. The latter is also shown to have better fracture properties than Ti-48 Al-2Cr-2Nb and TU48Al-1.5Cr extruded with a reduction ratio of 10:1. The implications of the results ...

On the Influence of Thermomechanical Processing on the Fatigue and Fracture Behavior of Gamma-Based Titanium Aluminides. IV. Effects of Alloying with V

ABSTRACT The effects or microstructure on the room - and elevated-temperature tensile and fracture properties of Ti-48Al-2.2V and Ti-48AI-3V are discussed in this paper, Microstructure is controlled by extrusion with different reduction ratios (10:1 and 14:1) and annealing in the α + γ and α2 + γ phase fields. V-containing Ti-48Al base alloys are shown to have attractive combinations of tensile and fracture properties only in the asextruded conditions. However, their tensile and fracture properties are degraded severely upon thermal exposure, which also results in grain boundary precipitation and fast microstructural transformations from nearly lamellar to nearly equiaxed structures. The degree of degradation is shown to increase with increasing V content and annealing duration. V-containing Ti-48Al base alloys are shown to have very limited potential for future alloy development.

Processing-Property-Microstructure Relationships in Tial-Based Alloys

ABSTRACTA range of TiAl-based alloys have been produced by plasma melting either small buttons (1kg samples) or ingots (up to 50kg). Some of the ingots have been atomised. The influence of thermomechanical processing on the microstructure of these materials has been assessed using optical and electron microscopy and the room temperature mechanical properties and creep strengths determined. It has been found that either through appropriate processing and/or through alloy development, it is possible to obtain alloys with room temperature strengths up to 1000MPa. Elongations of about 1% at room temperature have been obtained for alloys with this strength and this is coupled with significant improvements in creep strength over the reference alloy, Ti-48Al-2Mn-2Nb. The influence of the difficulty of slip transfer between gamma and alpha 2 has been assessed as one of the factors limiting ductility. Regions which are low in aluminium, which are present in the atomised powders initiate fracture at very low strains. These results are discussed in terms of the factors that control the strength and fracture behaviour of TiAl-based alloys.

The influence of thermo-mechanical processing on the hardness and microstructure of Beta-C titanium

Beta-C is a metastable titanium alloy with an alpha to beta transition temperature of 802 C and the high temperature beta phase readily retained at room temperature. The beta phase has a body centered cubic (bcc) structure and the alpha phase has a hexagonal close packed (hcp) structure. This alloy has a combination of good strength, ductility and fracture toughness as well as good corrosion resistance and low density. This has resulted in an interest in this alloy for use in a variety of industries. The Navy is investigating the use of this alloy as a replacement material for the steam catapults on aircraft carriers. The oil industry has found use for this alloy in tis transport piping systems, and a whole production schedule has been created for manufacturing Beta-C titanium for aircraft hydraulic lines. However, these properties are extremely sensitive to the thermo-mechanical processing (TMP) of the alloy. A study was undertaken in order to elucidate the effects of solution heat treatment, cold rolling and aging on the phase morphology, microstructure and hardness of Beta-C titanium. Preliminary results on the effects of solution heat treatment and cold rolling of this alloy are presented.

Influence of thermomechanical processing on the tensile and fatigue properties of a SiC particle reinforced aluminium alloy: Harris, S.J., McColl, I.R. and Huang, Z.W. Proc. Conf. Developments and Applications of Ceramics and New Metal Alloys, Quebec City, Quebec, Canada, 29 Aug.-2 Sept. 1993, pp. 117–126

Influence of thermomechanical processing on the tensile and fatigue properties of a SiC particle reinforced aluminium alloy: Harris, S.J., McColl, I.R. and Huang, Z.W. Proc. Conf. Developments and Applications of Ceramics and New Metal Alloys, Quebec City, Quebec, Canada, 29 Aug.-2 Sept. 1993, pp. 117–126

Influence of Thermomechanical Processing on the Mechanical and Physical Properties of Al-Mg-Si Alloy Containing Cr and Ti

Influence of Thermomechanical Processing on the Mechanical and Physical Properties of Al-Mg-Si Alloy Containing Cr and Ti

Influence of thermomechanical processing on martensitic transformation in 10Cr–18Mn austenitic steel

AbstractThe tensile properties of a metastable chromium–manganese steel are influenced by the deformation induced γ→e→α′ martensitic transformation. While beneficial in increasing the strain hardening rate and ultimate tensile strength, the presence of substantial amounts of e-martensite can lead to a brittle, transgranular fracture mode. An investigation has been made of the effect of prior thermomechanical processing on transformation and plastic deformation in a 10Cr–18Mn steel. Two different approaches were used: low temperature deformation and subsequent heat treatment, and high temperature deformation alone. The influence of these treatments on stress–strain behaviour and fracture is discussed. Transformation kinetics were studied by means of X-ray diffraction and magnetic measurements. Microstructural observations have shown that dislocation substructures introduced by prior deformation inhibit transformation by acting as barriers to the growth of e-platelets. The resultant decrease in the volume f...

Influence of thermomechanical processing on martensitic transformation in 10Cr–18Mn austenitic steel

The tensile properties of a metastable chromium–manganese steel are influenced by the deformation induced γ→ε→α′ martensitic transformation. While beneficial in increasing the strain hardening rate and ultimate tensile strength, the presence of substantial amounts of ε-martensite can lead to a brittle, transgranular fracture mode. An investigation has been made of the effect of prior thermomechanical processing on transformation and plastic deformation in a 10Cr–18Mn steel. Two different approaches were used: low temperature deformation and subsequent heat treatment, and high temperature deformation alone. The influence of these treatments on stress–strain behaviour and fracture is discussed. Transformation kinetics were studied by means of X-ray diffraction and magnetic measurements. Microstructural observations have shown that dislocation substructures introduced by prior deformation inhibit transformation by acting as barriers to the growth of ε-platelets. The resultant decrease in the volume fraction of martensite leads to an increase in ductility and the appearance of a region of non-uniform elongation before failure.MST/1280

Influence of thermomechanical processing on low cycle fatigue of prealloyed Ti-6AI-4V powder compacts

A wide range of microstructures was generated using various thermomechanical processing sequences in Ti-6A1-4V Rotating Electrode Process (REP) powder compacts of low contaminant content. Low cycle fatigue results were found to be superior to those in higher contaminant compacts tested in a previous program. All microstructural groups showed fatigue strengths equivalent to those found in wrought alloy, with the beta-annealed condition being lowest as expected. Alpha + beta work and solution treatment resulted in an excellent fatigue strength of 875 MN/m2 (127 ksi) at 105 cycles; 85 pct of the UTS. In the five conditions tested, the fatigue strength increased with increasing tensile strength, decreasing grain size, and increasing volume fraction of low aspect ratio primary alpha. Most crack initiation sites were observed at the specimen surface. Only alpha + beta worked and solution-treated material exhibited subsurface initiations, none of which was associated with any defect or with a lower fatigue life. Although compacts contained some tungsten particles, in no case were they associated with crack initiation sites, indicating that they were innocuous in the conditions evaluated.

Influence of thermomechanical processing on elevated temperature slow plastic flow properties of B2 aluminide Fe-39.8at.%Al

A study of the elevated temperature slow plastic flow properties of the B2 aluminide Fe-39.8at.%Al was undertaken. Polycrystalline materials possessing several different microstructures were produced by the hot extrusion of pre-alloyed powder and, in some cases, post-extrusion heat treatments. Compression tests were conducted in air at 1200, 1300 and 1400 K. Such testing revealed that the extrusion temperature affected the active deformation mechanisms where material extruded at 1505 K had a stress exponent about twice that of the intermetallic extruded at 1200 K. Grain size refinement to about 10 μm was found to strengthen the Fe-39.8at.%Al material; unfortunately the effectiveness of such strengthening is limited to a homologous temperature of about 0.75 for strain rates of commercial interest (less than 10 −7 s −1).

Influence of Thermo-Mechanical Processing on the Microstructure of Beryllia Dispersed Nickel Alloys

Currently there is a great interest in developing nickel base alloys with fine and uniform dispersion of stable oxide particles, for high temperature applications. It is well known that the high temperature strength and stability of an oxide dispersed alloy can be greatly improved by appropriate thermomechanical processing, but the mechanism of this strengthening effect is not well understood. This investigation was undertaken to study the dislocation substructures formed in beryllia dispersed nickel alloys as a function of cold work both with and without intermediate anneals. Two alloys, one Ni-lv/oBeo and other Ni-4.5Mo-30Co-2v/oBeo were investigated. The influence of the substructures produced by Thermo-Mechanical Processing (TMP) on the high temperature creep properties of these alloys was also evaluated.