Showing papers by "Terence G. Langdon published in 1991"
15 May 1991-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the major experimental observations in superplastic metals are summarized and the physical mechanisms of flow are discussed with reference to the behavior at high, intermediate and low strain rates, respectively.
Abstract: Superplasticity is an important mode of deformation in metallic alloys with very small grain sizes (usually less than 10 μm). In general, high elongations are observed over a rather limited range of intermediate strain rates and there is a decrease in the superplastic effect at both high and low strain rates. The major experimental observations in superplastic metals are summarized and the physical mechanisms of flow are discussed with reference to the behavior at high, intermediate and low strain rates, respectively. Superplastic-like behavior has been reported recently in some ceramics but the experimental evidence suggests that the mechanism of flow in these materials in not the as in metals.
128 citations
TL;DR: In this article, the authors reviewed the creep mechanisms in ceramics and compared experimental data, showing that there are three major types of creep behavior: a stress exponent close to 5 due to control by dislocation climb and fully ductile behaviour; a stress expander close to 3 due to controlling by climb from Bardeen-Herring sources and less than jive interpenetrating independent slip systems; and a stress extraction close to 1 due to diffusion creep.
Abstract: The creep mechanisms in ceramics are reviewed briefly and then compared with experimental data. It is shown that there are three major types of creep behaviour: a stress exponent close to 5 due to control by dislocation climb and fully ductile behaviour; a stress exponent close to 3 due to control by climb from Bardeen–Herring sources and less than jive interpenetrating independent slip systems; and a stress exponent close to 1 due to diffusion creep. The role of interface reaction control and the transitions from diffusion to power law creep are also examined.MST/1389
86 citations
TL;DR: In this paper, a detailed analysis of the creep behavior of copper in the intermediate temperature regime between 0.46 and 0.72 T m of the absolute melting point is presented, and it is concluded that high temperature climb is dominant in the power-law creep region, while obstacle-controlled glide occurring within the cell interiors is rate-controlling in the exponential creep regime.
Abstract: A detailed analysis of the creep behavior of copper in the intermediate temperature regime between 0.46–0.72 T m of the absolute melting point is presented. Several possible creep mechanisms are considered, and it is concluded that high temperature climb is dominant in the power-law creep region, while obstacle-controlled glide occurring within the cell interiors is rate-controlling in the exponential creep regime. A phenomenological model is proposed which assumes that cell boundaries within subgrains act as sources and obstacles to gliding dislocations. Dislocation annihilation is assumed to occur at the cell boundaries by climb and cross-slip. The implications of these results on the transition from power-law to exponential creep are examined.
20 citations
TL;DR: In this paper, microstructural observations reveal the formation of three types of slip features during the creep of polycrystalline copper at intermediate temperatures between 0.46 and 0.72 Tm, where Tm is the absolute melting point.
Abstract: Detailed microstructural observations reveal the formation of three types of slip features during creep of copper at intermediate temperatures between 0.46–0.72 Tm, where Tm is the absolute melting point. Single slip occurs at the higher temperatures and lower stresses with the slip lines being inhomogeneously distributed among the grains at the lower strains. Complex wavy slip features are observed at the higher temperatures, higher stresses and with increasing strains, thereby suggesting that cross-slip mechanisms may be important under these conditions. The absence of these slip patterns at the lower temperatures and higher stresses, when mainly multiple slip morphologies are observed, suggests that cross-slip mechanisms are likely to control the creep of polycrystalline copper only in a limited range of stresses and temperatures.
16 citations
3 citations
TL;DR: In this article, the authors describe a scenario in which, "a.k.a., ǫ-ǫ, Ã-a.d., Ã -a.b.
Abstract: 金属の超塑性は現在よく知られているが, 最近セラミックスでも超塑性に似た変形を示す報告がなされている。本論文では, 金属との違いを中心にセラミックスの超塑性について述べることにする.
2 citations
TL;DR: In this article, a strain rate change test is used to identify the process controlling the high temperature deformation of metals and metallic alloys, which does not require a testing machine having a high stiffness.
Abstract: The strain rate change test may be used to identify the process controlling thehigh temperature deformation of metals and metallic alloys. This paper presents a new analytical procedure whichhas several advantages: (i) it reduces the experimental diffculties inherent in an earlier analysis, (ii) it permits the incorporation of results from stress relaxation tests, and (iii) it does not necessarily require a testing machine having a highstiffness. The analytical procedure is described with reference to experimental data on pure Al and an Al-5.4 at% Mg solid solution alloy