The Effect of Surface Oxide Films on the Mechanical Behavior of NiAl

1984 ◽  
Vol 39 ◽  
Author(s):  
R. D. Noebe ◽  
R. Gibala
Keyword(s):  
Mechanical Behavior ◽  
Surface Film ◽  
Dislocation Core ◽  
The Body ◽  
Surface Films ◽  
Intermetallic Alloys ◽  
Body Centered Cubic ◽  
Cubic Metals ◽  
Bcc Metals ◽  
Ordered Intermetallic

ABSTRACTThin surface films have been shown to enhance the ductility and decrease the flow stress of several body-centered cubic metals at temperatures T < 0.2 Tm. The origin of this effect lies in the large difference in the intrinsic mobilities of edge and screw dislocations in body-centered cubic crystals. B2 ordered intermetallic alloys, although simple cubic in structure, are based on the body-centered cubic structure and have dislocation core structures, dislocation mobilities and temperature and orientation dependent deformation qualitatively similar to that of bcc metals. This investigation was initiated to examine possible effects of surface films on the mechanical behavior of B2 ordered intermetallic alloys, using oxidized NiAl as the initial material for investigation. Experiments were performed on an impure non-stoichiometric (47.1 at.% Al) single crystal material with an axial orientation near [123]. Surface film softening was observed at room temperature in compression at a strain rate of 2 x 10-4 s-1. Flow stresses of the oxide coated crystals were as much as 20% lower than those of identically prepared uncoated crystals. The strains to fracture of coated specimens were larger than those of uncoated specimens and in a few instances the ductility enhancement was as much as four times. Of the several oxides examined, the largest softening effects were found for a thermally deposited delta-A1203 film formed at 1000 °C for 1 hour. The current results for NiAl are compared to results previously obtained for bcc metals. Experiments which could further enhance the film softening effects observed in B2 ordered intermetallic alloys are suggested.

Voids in Irradiated Tungsten and Molybdenum

1969 ◽  
Vol 27 ◽  
pp. 190-191
Author(s):  
Robert C. Rau ◽  
Robert L. Ladd
Keyword(s):  
Melting Point ◽  
Fast Neutron ◽  
Neutron Irradiation ◽  
Elevated Temperatures ◽  
Irradiation Temperature ◽  
The Body ◽  
Face Centered Cubic ◽  
Body Centered Cubic ◽  
Cubic Metals ◽  
Face Centered

Recent studies have shown the presence of voids in several face-centered cubic metals after neutron irradiation at elevated temperatures. These voids were found when the irradiation temperature was above 0.3 Tm where Tm is the absolute melting point, and were ascribed to the agglomeration of lattice vacancies resulting from fast neutron generated displacement cascades. The present paper reports the existence of similar voids in the body-centered cubic metals tungsten and molybdenum.

Temperature and Orientation Dependence of Surface Film Effects in Single Crystal Nial

1986 ◽  
Vol 81 ◽  
Author(s):  
R.D. Noebe ◽  
J.T. Kim ◽  
R. Gibala
Keyword(s):  
Single Crystal ◽  
Crystallographic Orientation ◽  
Surface Film ◽  
Orientation Dependence ◽  
Surface Films ◽  
Temperature Dependent ◽  
Paper Surface ◽  
Bcc Metals ◽  
Coated Materials ◽  
Ordered Alloys

AbstractDuring deformation of bcc metals and bcc-based ordered alloys, conditions of elastic and plastic constraint associated with the presence of thin adherent surface films can be responsible for introducing increased densities of mobile dislocations in the metal, resulting in enhanced ductility and reduced yield and flow stresses of the film-coated materials. In the present paper, surface film effects were investigated as a function of temperature and crystallographic orientation for single crystal β-NiAl. Appreciable temperature-dependent and orientation-dependent surface film effects were observed, as were significant effects of film adherence on the observation of surface film softening.

Dislocation core structure in ordered intermetallic alloys

1991 ◽  
Vol 1 (6) ◽  
pp. 997-1014 ◽  
Author(s):  
R. Pasianot ◽  
D. Farkas ◽  
E. J. Savino
Keyword(s):  
Dislocation Core ◽  
Core Structure ◽  
Intermetallic Alloys ◽  
Ordered Intermetallic ◽  
Dislocation Core Structure

scholarly journals Non-glide effects and dislocation core fields in BCC metals

2019 ◽  
Vol 5 (1) ◽  
Author(s):  
Antoine Kraych ◽  
Emmanuel Clouet ◽  
Lucile Dezerald ◽  
Lisa Ventelon ◽  
François Willaime ◽  
...  
Keyword(s):  
First Principles ◽  
Yield Criterion ◽  
Constitutive Models ◽  
Dislocation Core ◽  
First Principles Calculations ◽  
Body Centered Cubic ◽  
Physical Origin ◽  
Bcc Metals ◽  
Energy Models ◽  
Eshelby Inclusion

AbstractA hallmark of low-temperature plasticity in body-centered cubic (BCC) metals is its departure from Schmid’s law. One aspect is that non-glide stresses, which do not produce any driving force on the dislocations, may affect the yield stress. We show here that this effect is due to a variation of the relaxation volume of the $$1/2\langle 111\rangle$$1∕2⟨111⟩ screw dislocations during glide. We predict quantitatively non-glide effects by modeling the dislocation core as an Eshelby inclusion, which couples elastically to the applied stress. This model explains the physical origin of the generalized yield criterion classically used to include non-Schmid effects in constitutive models of BCC plasticity. We use first-principles calculations to properly account for dislocation cores and use tungsten as a reference BCC metal. However, the methodology developed here applies to other BCC metals, other energy models and other solids showing non-glide effects.

An Analysis of Lattice Dynamical Angular Force Models for Body Centered Cubic Metals

1979 ◽  
Vol 34 (6) ◽  
pp. 721-723
Author(s):  
R. N. Khanna ◽  
R. P. S. Rathore
Keyword(s):  
General Equilibrium ◽  
Pair Potential ◽  
Dynamical Behaviour ◽  
Body Centered Cubic ◽  
Axially Symmetric ◽  
Equilibrium Conditions ◽  
Central Pair ◽  
Electron Pressure ◽  
Cubic Metals ◽  
Bcc Metals

Abstract Present angular force models for lattice dynamical behaviour of body centered cubic (bcc) metals have been analysed for the satisfaction of rotational invariance and general equilibrium conditions. It has been found that most of the angular force models (except that due to Clark et al.) are deficient and leave the lattice under stress. Further it has been inferred that either the axially symmetric or the central pair potential schemes, incorporating the concept of electron pressure, provide the realistic picture of lattice excitations in metals.

Surface Films on Zircaloy-2 Samples Cracked in Neutral Aqueous NaCl by Stress Corrosion

1973 ◽  
Vol 31 ◽  
pp. 46-47
Author(s):  
R.A. Ploc
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Film Thickness ◽  
Stress Corrosion ◽  
Zirconium Dioxide ◽  
Surface Film ◽  
Surface Films ◽  
Continuous Layer ◽  
Transmission Electron ◽  
Product Film

Samples of low-nickel Zircaloy-2 (material MLI-788-see(1)), when anodically polarized in neutral 5 wt% NaCl solutions, were found to be susceptible to pitting and stress corrosion cracking. The SEM revealed that pitting of stressed samples was occurring below a 2000Å thick surface film which behaved differently from normal zirconium dioxide in that it did not display interference colours. Since the initial film thickness was approximately 65Å, attempts were made to examine the product film by transmission electron microscopy to deduce composition and how the corrosion environment could penetrate the continuous layer.

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