Fernando Carreño

Microstructure and fracture properties of an ultrahigh carbon steel–mild steel laminated composite

Abstract A seven layer steel based (mild steel and ultrahigh carbon steel, UHCS) laminated composite was processed by roll bonding. Impact properties were improved in comparison with the UHCS. Delamination plays an important role by deflecting cracks, absorbing energy and imposing the nucleation of new cracks in the next material layer.

Grain structure and microtexture after high temperature deformation of an Al-Li (8090) alloy

The dynamic recrystallization of an aluminum‐lithium (8090) alloy at high temperatures (380‐570°C) at a strain rate of 0.8 s 1 was studied. The microstructure of the annealed sample fragmented during deformation at high temperature to form new small recrystallized grains. The stress versus strain curves showed stress oscillations. The texture of the annealed material at 440°C is defined by a rotated cube component. This component rotates toward a cube component in the course of deformation at 440 and 550°C. Microtexture determinations revealed that the annealed sample as well as the deformed samples showed a high amount of low-S, coincident site lattice misorientations, particularly S1. Annealed samples are characterized by S1, 5, 7, 9, 13, 21 and 29 boundaries whereas S1, 3 and 13 boundaries are characteristic of the deformed samples.

Influence of interfaces on the mechanical properties of ultrahigh carbon steel multilayer laminates

Abstract To improve impact and flexure properties of ultrahigh carbon steel (UHCS-1.3 wt.% C), a multilayer laminate consisting of 20 layers of the same UHCS has been processed by hot rolling. Two different rolling conditions gave rise to “soft” and “severe” laminates. The toughness of the “soft” laminate, measured by impact test absorbed energy, was more than forty times higher than that of the monolithic UHCS and three times higher than that of mild steels. In contrast, the “severe” laminate showed no increase in toughness with respect to the monolithic UHCS. This large difference in behaviour was studied by means of shear and bend tests, which gave valuable information on bond quality and delamination.

Texture Stability of a Rapidly Solidified Dispersion Strengthened Al-Fe-V-Si Material

The authors gratefully acknowledge the support of the Comision Interministerial de Ciencia y Tecnologia (CICYT) under Grant No. MAT94/0888.

High temperature mechanical behaviour of δ–γ stainless steel

AbstractThe deformation behaviour of a duplex stainless steel has been investigated by tensile and torsion tests at temperatures ranging from 1000 to 1275°C. The microstructure of the as received material consists of elongated islands of austenitic grains in a more or less continuous ferrite matrix. This microstructure remains essentially constant during deformation by tensile strain rate change tests. Deformation occurs by a slip creep process in most of the range of strain rates tested (n = 5) with a transition to a grain boundary sliding mechanism in the lower stress regime. On the other hand, dynamic recrystallisation starts after a critical strain during torsion testing. The flow stress decreases to a steady state value associated with a fine and stable microstructure. The deformation behaviour is characterised by a stress exponent of about 2·5–3, which suggests a contribution to deformation of both, slip creep and grain boundary sliding mechanisms. An activation energy for deformation of 370 kJ mol-...

Microstructural changes during high temperature deformation of an Al-Li(8090) alloy

In this work, the high temperature tensile behavior of an aluminum-lithium (8090) alloy is studied at various strain rates and temperatures. In particular, special attention was paid to the oscillations observed in the true stress versus strain curves at high strain rate, 0.8 s{sup {minus}1}, and high temperatures in excess of 380 C (> 0.57 T{sub m}, where T{sub m} is the melting temperature). The changes in the microstructure were analyzed and correlated to the flow curves of the deformed samples.

Elevated temperature creep behavior of three rapidly solidified Al-Fe-Si materials containing Cr, Mn, or Mo

Abstract Research on the high temperature creep behavior of three rapidly solidified Al-Fe-X-Si (where X = Cr, Mn or Mo) dispersion strengthened materials with three different alloying compositions has been conducted. Firstly, microstructural examinations have been carried out on the as-received, thermally treated and tested samples. The microstructure consists of a fine Al matrix embedding small round-shaped Al 12 (Fe,X) 3 Si and Al 13 (Fe,X) 4 dispersoids. Grain sizes ranging from 0.85 to 1.45 μm and dispersoid sizes ranging from 45 to 54 nm were observed. Secondly, tensile tests were performed at high temperature from 573 to 823 K at strain rates ranging from 2.5×10 −6 to 10 −2 s −1 . The experimental data exhibited high apparent stress exponent, n ap , and high activation energy, Q ap . The rnicrostructure remained stable and fine after testing. The results are analyzed by means of various models used in the literature.

High temperature deformation behavior of an Al-Fe-V-Si alloy

Abstract The deformation behavior between 250 and 550 °C of a fine-grained (0.5 μm) AlFeVSi alloy strengthened by fine particles (50 nm) and processed by a rapid solidification route was investigated. The material is characterized by high stress exponents and activation energies for creep, which are strongly dependent on temperature. Two different approaches are considered to explain the deformation behavior of the alloy: a constant-structure, slip creep mechanism with a threshold stress; and a slip creep mechanism involving dislocation detachment from dispersoid particles, as suggested by transmission electron microscopy.

Deformation behavior during hot torsion of an ultrahigh carbon steel containing 1.3 wt. % C

Abstract The torsion behavior of an ultrahigh carbon steel containing 1.3 wt.% C has been studied at high strain rates (2–26 s–1) and high temperatures (900–1200 °C). Adiabatic heating strongly affects the shape of the stress–strain curves. Grain size measurements at strains of e = 2 and e = 5 reveal that the austenite grain size does not change between these two strains and is finer than the initial austenite grain size. This is an indication that a recrystallization process took place in the interval of strains between epeak and e = 2 and that the deformation state associated to the strains of e = 2 and e = 5 can be considered as steady state. Stress–strain rate relations have been analysed for epeak, e = 2 and e = 5. It has been found that data obtained at epeak correlate well with a lattice diffusion-controlled dislocation creep process. On the other hand, analysis of the stress–strain rate relations found at the steady state indicated that the deformation occurs by the contribution of two independent...

Threshold stresses in high temperature deformation of dispersion strengthened aluminum alloys

Creep data of five dispersion-strengthened aluminum materials were analyzed by means of well known diffusion controlled slip creep mechanisms incorporating a threshold stress. It is shown that the threshold stress that has to be introduced into such mechanisms to fit the creep data is strongly temperature dependent. Such temperature dependence cannot be explained by the various models used in the literature.