P.W. Kao

Effect of die angle on the deformation texture of copper processed by equal channel angular extrusion

Abstract The deformation texture of copper processed by equal channel angular extrusion (ECAE) was investigated with two different die angles. For specimens deformed by different die angles, the preferred orientations were found different, which was attributed to the different orientations of the shear plane with respect to the measuring plane for different die angles. It has been demonstrated that the ECAE deformation texture resulted from different die angles can be analyzed in terms of the crystallographic orientations of the shear plane and the shear direction in ECAE. The shear direction in ECAE was found essentially parallel to the 〈110〉 direction in copper. This study has confirmed that the ECAE technique does produce a deformation texture similar to that of simple shear (torsion).

Characteristics of submicron grained structure formed in aluminum by equal channel angular extrusion

Abstract This work has shown that submicron grained (∼0.35 μm) structure can be formed by applying equal channel angular extrusion (ECAE) to e =8 at room temperature. In addition, the resulted submicron grained structure is characterized by a random microtexture. Based on the observation, it is suggested that grain subdivision and texture evolution, as well as local boundary migration are the possible mechanisms involved in the formation of submicron grains during severe plastic deformation.

Microstructure and flow stress of copper deformed to large plastic strains

Abstract Copper was deformed to large plastic strain ( e >10) by equal channel angular extrusion at room temperature. The flow stress reaches a peak value at strain near 4 followed by slight softening. The dominant deformation structure for strain greater than 2 is lamellae. As strain increases, the lamellar thickness decreases to a value about 0.2 μm. Small number of recrystallized grains formed in specimens deformed to e >10.

Microstructure and tensile properties of a commercial 5052 aluminum alloy processed by equal channel angular extrusion

A commercial 5052 aluminum alloy was processed by equal channel angular extrusion at 423 K to a strain of ∼8. The as-extruded microstructure is quite uniform, which can be characterized as a mixture of elongated and equiaxed subgrains with submicrometer size and high misorientations. In static annealing, the as-extruded structure is quite stable at 423 K and shows slow coarsening at 473 K. The microstructure resulted from more ECAE passes (higher strain) is more readily to develop a uniform structure of equiaxed grains in static annealing. Very high strength (394 MPa yield stress and 421 MPa ultimate tensile strength) and reasonable ductility (10.5% tensile elongation) can be obtained in this non-heat treatable aluminum alloy. The high strength can be related to the structure of submicron-sized subgrains (grains). To increase the strain from 4 to 8 is beneficial for producing finer structure and higher strength.

Effect of fiber bridging on the fatigue crack propagation in carbon fiber-reinforced aluminum laminates

Abstract A superior crack propagation resistance was observed on various carbon fiber-reinforced aluminum laminates (CARALL) under tension-tension fatigue. It might be attributed to the restraint on the crack opening imposed by intact fibers in the crack wake. These fibers bridging the crack could reduce the effective stress intensity factor actually experienced by the crack tip. Based on the measurement of crack length and delamination size, the effective stress intensity range, ΔKeff, of fatigue-damaged CARALL laminate was calculated by using a simplified analytical model. It was shown that the fatigue crack propagation rate in CARALL could be expressed as a unique function of the calculated ΔKeff, which agree well with the Paris equation for the unreinforced aluminum alloy. This result confirmed the applicability of this simplified analytical model in CARALL laminates.

Thermal cycling induced deformation and damage in carbon fiber reinforced copper composite

Abstract A unidirectional Cu/C composite with 40% T300 carbon fibers was found to have very low CTE, average about 1×10 −6 K −1 over the temperature range of 300–1073 K. Dimensional stability of the composite was investigated under thermal cycling between 0.35 and 0.8 of the matrix homologous temperature. Void formation has been identified as the major damage mechanism in the Cu/C composite under thermal cycling

The strengthening effect of Al3Ti in ultrafine grained Al-Al3Ti alloys

Aluminum alloys prepared by mechanical alloying (MA) usually contain significant amount of ultrafine carbide and oxide dispersoids, which play vital roles in obtaining the fine grains and high strength in these alloys. The stiffness and strength of such alloys can be further improved by adding aluminum-transition metal intermetallic phases. As compared to most aluminum-rich intermetallic phases, Al{sub 3}Ti has many attractive properties. The unique microstructure of the MA Al-Al{sub 3}Ti alloys, i.e., submicron grain size and uniform dispersion of fine carbides and oxides, is quite common for alloys produced by the MA process. According to the characteristics of the microstructure, the MA Al-Al{sub 3}Ti alloy may be considered as a fine Al-Al{sub 3}Ti two-phase composite, in which the aluminum matrix is further strengthened by the fine dispersoids of carbide and oxide. Such a two-phase composite with submicron sized grains for both phases cannot be easily obtained by other means. Therefore, it is worthwhile to study the strengthening mechanisms in the MA Al-Al{sub 3}Ti alloys, especially the role of the submicron sized reinforcements, Al{sub 3}Ti.

Microstructural characteristics of ultrafine-grained aluminum produced by equal channel angular extrusion

Abstract The microstructures of pure aluminum produced by equal channel angular extrusion (ECAE) with routes Bc and C were characterized quantitatively by the use of transmission electron microscopy. A comparison with the results of cyclic-extrusion–compression reported in the literature is also presented, which indicates that ECAE is more effective in generating high angle boundaries.

Effect of alloying additions on the κ phase precipitation in austenitic Fe-Mn-Al-C alloys

Aging of Fe-30Mn-10Al-1C-1Si alloy at 550--700 C causes extensive precipitation of the [kappa] phase at austenite grain boundaries as well as within austenite grains, which will be named as intergranular and intragranular [kappa] phase respectively. The formation of fine intragranular [kappa] phase is considered to be a possible hardening mechanism for this alloy system. However, it has been shown that the presence of intragranular [kappa] phase can cause brittle fracture before yielding at subzero temperatures. On the other hand, the intergranular [kappa] phase alone can result in a severe loss in impact energy at both room and subzero temperatures. Owing to the importance of the precipitation of [kappa] phase on the mechanical properties, a better knowledge of the alloying effect on the precipitation is important for the further development of this alloy system. In the present work, a systematic study of the effect of alloying elements, aluminum and carbon in particular, on the precipitation of [kappa] phase was carried out over a range of composition within which a single phase austenite is formed upon solution treating and quenching.

Mechanical properties of Fe30Mn10Al1C1Si alloy

Abstract The present work is a study of the tensile properties from 77 to 1123 K and the impact toughness from 77 K to room temperature of an austenitic Fe30Mn10Al1C1Si alloy. It was found that for temperatures below 773 K this alloy possesses high strength and good ductility, but exhibits a ductile-to-brittle transition in impact toughness at temperatures lower than 233 K. For the solution-treated condition, a minimum ductility is observed around 923 K. Transgranular cleavage cracking is the predominant fracture mode for solution-treated specimens tensile-tested at 77 K. The cleavage facets are identified as the {111} planes. This alloy shows considerable age-hardening capability. Aging at 823 K for 16 h results in an increase in yield stress of about 90% for temperatures ranging from 298 to 773 K, but causes brittle fracture at lower temperatures.