Yield Stress Anomaly Research Articles

Nature of Slip in γ-Titanium Aluminide Above the Yield Stress Anomaly Temperature

ABSTRACTCrystals of γ-TiAl, containing ∼54.5 at% Al, with various orientations were deformed at different temperatures and examined by transmission electron microscopy (TEM). It was found that while in many cases slip and climb of ordinary dislocations tend to predominate, slip by [001] dislocations can be important also. The occurrence of [001] slip has not been reported before. The values of critical resolved shear stress were determined and strong locks on [001] dislocations have been identified as local segments of ½ ⟨112] dislocations arising from interactions between [001] and ½⟨110] dislocations.

Size Scaling in the Self-Immortalization of Superdislocations in the L12 Compounds Displaying the Yield Strength Anomaly

ABSTRACTA simple statistical analysis of the distribution of superkinks along a single superdislocation is presented. This analysis is then used to estimate the rate of self-immobilization of superdislocations. The self-immobilization rate decreases exponentially with increasing superdislocation length. The implications for experiment are discussed.

Peierls friction stresses and dynamic strain ageing in TiAl and Fe-30at.% Al alloys

In situ straining experiments show microscopic evidence of dynamic strain ageing in TiAl and Fe-30at.% Al, at intermediate temperatures. The multiplication and the exhaustion of the mobile dislocations are studied, and the results indicate that strain-hardening, strain-rate sensitivities, yield-stress anomalies and dynamic strain ageing are strongly correlated.

Dislocation Dynamics and Yield Stress Anomalies in Intermetallic Alloys

AbstractMany intermetallic alloys with L12, L10and BCC related structures exhibit yield-stress anomalies, which have strong influence on their mechanical properties at intermediate temperatures. A short review is made of the anomalous glide systems in various intermetallics. They are shown to exhibit several common characteristics, which allow it to classify them into three groups with possibly similar dislocation mechanisms. In the second half, the well-known case of octahedral glide in Ni3Al is considered again, and a new model is proposed, based on the formation and the unlocking process of incomplete Kear-Wilsdorf locks by a double cross-slip mechanism. This model is supported by several microscopic and macroscopic observations including “in situ” straining experiments in a TEM. It accounts for the positive temperature dependence of the yield-stress with fairly good orders-of-magnitude estimates of the stress. It also explains satisfactorily the small stress-strain rate sensitivity and the transient effects.

The Yield Stress Anomaly in Fe-Al Alloys: The Role of the Local Climb Locking Mechanism

AbstractA detailed examination of the variation of yield stress with temperature in an Fe3Al alloy shows a maximum at a temperature of about 500°C, slightly below the critical temperature for loss of DO3 order. At this temperature the dislocations present in the material change from being <111= superdislocations separated by APB to being single dislocations with Burgers vector <100=. At slightly lower temperatures the superdislocations become pinned by a local climb process involving point defect transfer between the partial dislocations.Analysis of the forces between the dislocations which induce the local climb locking process allows an estimation of the role which will be played by variations in composition of the Fe-Al alloy considered, changes in deformation rate and orientation of the applied stress.Examination of data available in the literature shows that each of the three aspects discussed, namely the influence of variations in ordered state, in Al content over the range 25% to 50%, or additions of alloying elements such as Si, straining at very fast or at slow rates, and stressing along different crystallographic axes, is completely consistent with the model proposed.

Mechanisms of yield stress anomalies in beryllium and Ni 3Al

The origin of the anomalous increase in yield stress with increasing temperature observed in many materials is discussed with reference to the well-documented cases of prismatic glide in beryllium and octahedral glide in Ni 3Al and related alloys. The main experimental results are reviewed, and compared with the most current models. The outlines of a new model are presented for Ni 3Al, based on the same general principles as that derived in beryllium.

The Yield Stress Anomaly in Ll2 Alloys

The Yield Stress Anomaly in Ll2 Alloys

Report of the discussion at the “Round Table on the Yield Stress Anomaly”

The conference organisers included a discussion period on the yield stress anomaly in metals and ordered alloys, “animated” by Professor Sir Peter Hirsch and Dr. D. Dimiduk. The existing models were shown to be incompatible with the observed small strain-rate dependence of the yield stress. Alternative models were discussed, and difficulties and outstanding problems identified.

The Low-Temperature Yield Stress Anomaly in Metals and Alloys

physica status solidi (a)Volume 74, Issue 1 p. 11-42 Review Article The Low-Temperature Yield Stress Anomaly in Metals and Alloys T. A. Parkhomenko, T. A. Parkhomenko Physico-Technical Institute of Low Temperatures, Academy of Sciences of the Ukrainian SSR, Kharkov Search for more papers by this authorV. V. Pustovalov, V. V. Pustovalov Physico-Technical Institute of Low Temperatures, Academy of Sciences of the Ukrainian SSR, Kharkov Search for more papers by this author T. A. Parkhomenko, T. A. Parkhomenko Physico-Technical Institute of Low Temperatures, Academy of Sciences of the Ukrainian SSR, Kharkov Search for more papers by this authorV. V. Pustovalov, V. V. Pustovalov Physico-Technical Institute of Low Temperatures, Academy of Sciences of the Ukrainian SSR, Kharkov Search for more papers by this author First published: 16 November 1982 https://doi.org/10.1002/pssa.2210740102Citations: 29 Lenin Prospekt 47, Kharkov 164, USSR. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume74, Issue116 November 1982Pages 11-42 RelatedInformation

Deformation of tungsten single crystals from −77°C to 800°C

Single crystals of tungsten prepared by electron beam melting were tested in tension over a temperature range from −77°C to + 800°C. The temperature dependence of the yield stress was found to be similar to that of polycrystalline tungsten. At temperatures below 300°C, the temperature dependence of the yield stress of both materials is about the same. In an intermediate temperature region from 300°C to 800°C, yield stress anomalies (peaks and valleys) are found for both the single crystal and the polycrystalline tungsten. These yield stress effects are attributed to the precipitation of interstitials.