scholarly journals The role of Ca, Al and Zn on room temperature ductility and grain boundary cohesion of magnesium

Author(s):  
Supriya Nandy ◽  
Shao-Pu Tsai ◽  
Leigh Stephenson ◽  
Dierk Raabe ◽  
Stefan Zaefferer
Author(s):  
J. E. Doherty ◽  
A. F. Giamei ◽  
B. H. Kear ◽  
C. W. Steinke

Recently we have been investigating a class of nickel-base superalloys which possess substantial room temperature ductility. This improvement in ductility is directly related to improvements in grain boundary strength due to increased boundary cohesion through control of detrimental impurities and improved boundary shear strength by controlled grain boundary micros true tures.For these investigations an experimental nickel-base superalloy was doped with different levels of sulphur impurity. The micros tructure after a heat treatment of 1360°C for 2 hr, 1200°C for 16 hr consists of coherent precipitates of γ’ Ni3(Al,X) in a nickel solid solution matrix.


1990 ◽  
Vol 213 ◽  
Author(s):  
T. K. Chaki

ABSTRACTInterstitial boron atoms are known to increase room temperature ductility in Ni-rich Ni3Al and Ni3Si. Inerstitial carbon atoms increase ductility in Ni-rich Ni3Si, but not in Ni3Al. It is argued that grain boundary segregation of B or C is not the cause of the increase in ductility. Instead, strong Ni-B bonding and antisite Ni defects reduce the strength of directional Ni-Al bonding in ordered Ni3Al so that Ni and Al atoms can relax more easily to fill up the microcavities at the grain boundaries, thereby strengthening the boundaries. The reduced Ni-Al bonding will also enhance the ductility in the interior of the grains so that dislocations can be easily generated to shield the tips of the cracks at the grain boundary. In Ni3Si, strong Si-C bonds distort the directionality of Ni-Si bonding. Evidence for this model is presented. Estimates of the concentration of interstitial atoms to achieve maximum ductility are made and the estimate agrees well with the experimental value.


2002 ◽  
Vol 718 ◽  
Author(s):  
Sang-Bop Lee ◽  
Kwang-Ho Lee ◽  
Hwan Kim

AbstractThe effect of changing sintering temperature on the grain boundary properties and the room temperature resistivity (ρRT) of Pb(Fe1/2Nb1/2)O3 (PFN) was investigated. Monitering the temperature dependence of resistivity showed that the ρRT's of 1050°C and 1150°C-sintered specimen were 1011ΩEcm and 104ΩEcm respectively, but the resistivity above 300°C became nearly identical. The previous model, that the low resistivity of PFN is due to the electron hopping between Fe2+ and Fe3+ driven by the reduction of PFN, couldn't explain this phenomenon, and the reconsideration of the Fe reduction revealed that the difference of electron concentration between the 1050°C and 1150°C-sintered specimen couldn't exceed one order of magnitude. The role of the grain boundary was introduced in order to account for this phenomenon.


Author(s):  
A.H. Advani ◽  
L.E. Murr ◽  
D. Matlock

Thermomechanically induced strain is a key variable producing accelerated carbide precipitation, sensitization and stress corrosion cracking in austenitic stainless steels (SS). Recent work has indicated that higher levels of strain (above 20%) also produce transgranular (TG) carbide precipitation and corrosion simultaneous with the grain boundary phenomenon in 316 SS. Transgranular precipitates were noted to form primarily on deformation twin-fault planes and their intersections in 316 SS.Briant has indicated that TG precipitation in 316 SS is significantly different from 304 SS due to the formation of strain-induced martensite on 304 SS, though an understanding of the role of martensite on the process has not been developed. This study is concerned with evaluating the effects of strain and strain-induced martensite on TG carbide precipitation in 304 SS. The study was performed on samples of a 0.051%C-304 SS deformed to 33% followed by heat treatment at 670°C for 1 h.


Author(s):  
Bradley L. Thiel ◽  
Chan Han R. P. ◽  
Kurosky L. C. Hutter ◽  
I. A. Aksay ◽  
Mehmet Sarikaya

The identification of extraneous phases is important in understanding of high Tc superconducting oxides. The spectroscopic techniques commonly used in determining the origin of superconductivity (such as RAMAN, XPS, AES, and EXAFS) are surface-sensitive. Hence a grain boundary phase several nanometers thick could produce irrelevant spectroscopic results and cause erroneous conclusions. The intergranular phases present a major technological consideration for practical applications. In this communication we report the identification of a Cu2O grain boundary phase which forms during the sintering of YBa2Cu3O7-x (1:2:3 compound).Samples are prepared using a mixture of Y2O3. CuO, and BaO2 powders dispersed in ethanol for complete mixing. The pellets pressed at 20,000 psi are heated to 950°C at a rate of 5°C per min, held for 1 hr, and cooled at 1°C per min to room temperature. The samples show a Tc of 91K with a transition width of 2K. In order to prevent damage, a low temperature stage is used in milling to prepare thin foils which are then observed, using a liquid nitrogen holder, in a Philips 430T at 300 kV.


Author(s):  
Jin Young Kim ◽  
R. E. Hummel ◽  
R. T. DeHoff

Gold thin film metallizations in microelectronic circuits have a distinct advantage over those consisting of aluminum because they are less susceptible to electromigration. When electromigration is no longer the principal failure mechanism, other failure mechanisms caused by d.c. stressing might become important. In gold thin-film metallizations, grain boundary grooving is the principal failure mechanism.Previous studies have shown that grain boundary grooving in gold films can be prevented by an indium underlay between the substrate and gold. The beneficial effect of the In/Au composite film is mainly due to roughening of the surface of the gold films, redistribution of indium on the gold films and formation of In2O3 on the free surface and along the grain boundaries of the gold films during air annealing.


Author(s):  
Ian M. Anderson

B2-ordered iron aluminide intermetallic alloys exhibit a combination of attractive properties such as low density and good corrosion resistance. However, the practical applications of these alloys are limited by their poor fracture toughness and low room temperature ductility. One current strategy for overcoming these undesirable properties is to attempt to modify the basic chemistry of the materials with alloying additions. These changes in the chemistry of the material cannot be fully understood without a knowledge of the site-distribution of the alloying elements. In this paper, the site-distributions of a series of 3d-transition metal alloying additions in B2-ordered iron aluminides are studied with ALCHEMI.A series of seven alloys of stoichiometry Fe50AL45Me5, with Me = {Ti, V, Cr, Mn, Co, Ni, Cu}, were prepared with identical heating cycles. Microalloying additions of 0.2% B and 0.1% Zr were also incorporated to strengthen the grain boundaries, but these alloying additions have little influence on the matrix chemistry and are incidental to this study.


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