Showing papers on "Hardening (metallurgy) published in 1968"
TL;DR: In this article, a solute-clustering model is proposed for grain boundary quench-hardening based on preferential solutevacancy interactions and non-ideal thermodynamic behavior of the binary system.
226 citations
TL;DR: In this article, the authors examined the temperature dependence predicted by theories of dispersed barrier hardening and discussed limitations of the theories and clarified several misconceptions on the theories, including that it is not possible to select one of several interaction potentials on the basis of an experimentally obtained stress-temperature relationship.
Abstract: This paper examines the temperature dependence predicted by theories of dispersed barrier hardening. Most of interaction potentials employed in the theories are similar. It is not possible to select one of several interaction potentials on the basis of an experimentally obtained stress‐temperature relationship. This paper discusses limitations of the theories and clarifies several misconceptions on the theories.
126 citations
TL;DR: In this article, it was found that at room temperature the critical resolved shear stress (CRSS) is a linear function of the concentration of nitrogen plus residual carbon, and the alloy hardening is 460,000 kgf/cm2 per unit atomic fraction of interstitials.
119 citations
TL;DR: In this paper, the effects on deformational behavior produced by the addition of sand particles to the ice matrix were studied using axial stress creep tests and constant axial strain-rate tests.
Abstract: The mechanical properties of a saturated frozen sand were studied using constant axial stress creep tests and constant axial strain-rate tests. Observation of the effects on deformational behavior produced by the addition of sand particles to the ice matrix led to an analysis useful in predicting creep rates for a constant stress and stress levels for a constant strain rate. The relationship between strain rate and stress for polycrystalline ice considers a strain dependent hardening term and a strain energy dependent softening term. Parameters of the equation include stress and temperature. Stress factors, dependent on sand volume concentration and friction and dilatancy of the sand, are used in conjunction with the equation for polycrystalline ice to give predictions of the mechanical behavior of the sand-ice system. These are in reasonable agreement with experimental data.
108 citations
TL;DR: In this article, the authors investigated the nature and magnitude of radiation hardening in an 18-8 type austenitic stainless steel after a high neutron exposure (1.4 × 1022 n/cm2, E > 0.18 MeV) near one-half the absolute melting temperature (532°C).
87 citations
TL;DR: In this paper, a series of iron-carbon and iron-nickel-carbon steels have been investigated in order to assess the relative contribution of the following to the strength of martensite: 1) solid solution hardening by carbon, 2) carbon in the form of precipitates or segregates, and 3) the substructure of the martensites, i.e. dislocation tangles or internal twinning.
72 citations
TL;DR: In this article, a precipitated phase was identified as Al 11 V by electron diffraction and was shown to have a hardness three times that of annealed aluminum and retained this hardness after high-temperature heat treatments.
55 citations
TL;DR: In this article, a numerical method for the boreexpanding test of sheet metals is applied to the strain-hardening characteristics of the material and the stress and strain distributions and the maximum load in the relevant test have been calculated by use of the incremental theory of plasticity.
52 citations
52 citations
TL;DR: In this article, the authors generalize the concept of kinematic hardening for the case when the stress-strain law is nonlinear, and show that although a yield condition of the form with κ constant or variable cannot represent non-linear KH, at least one yield condition, where κ is a constant, represents such hardening.
Abstract: Traditionally, the kinematic hardening assumption is used in conjunction with an assumption that the stress-strain curve for simple tension can be approximated by a bilinear curve. This paper generalizes the concept of kinematic hardening for the case when the stress-strain law is nonlinear. It is shown that although a yield condition of the form
with κ constant or variable cannot represent non-linear kinematic hardening, at least one yield condition of the form
where
, represents such hardening.
51 citations
TL;DR: In this paper, the energy fluctuations a dislocation segment encounters on moving through a crystal due to random composition fluctuations are calculated, as a result of these energy fluctuations, the dislocation line becomes slightly kinky.
Abstract: The stress required to move a dislocation in a solid‐solution alloy is considered. The analysis is based on a model which is particularly applicable to concentrated solid solutions. The energy fluctuations a dislocation segment encounters on moving through a crystal due to random composition fluctuations are calculated. In this paper it is assumed that only the elastic constants are affected by the variations in composition. As a result of these energy fluctuations, the dislocation line becomes slightly kinky. It is possible to calculate the mean energy barrier for motion of a double kink and also the average dimension of the double kink. The shear stress at 0°K is then determined. The results are compared to experimental data available for Au–Ag alloys and to other hardening theories.
TL;DR: In this article, it was shown that cavities form on grain boundaries and cause a decrease in density during the fatigue of copper at elevated temperatures, and the fractional change in density is directly proportional to time for tests in which the plastic strain amplitude remains constant.
Abstract: During the fatigue of copper at elevated temperatures cavities form on grain boundaries and cause a decrease in density. The fractional change in density is directly proportional to time for tests in which the plastic strain amplitude remains constant. In constant-stress tests, when the stress is sufficient to cause appreciable hardening, the fractional change in density is approximately proportional to (time)⅔. For the majority of the tests the activation energy of the growth process is 24.2 kcal.mole−1; this and other evidence suggests that growth depends on a grain-boundary diffusion mechanism as well as on the migration of vacancies created by fatigue. The results are interpreted on the basis of a model in which defects absorbed by grain-boundary migration contribute to cavity growth.
TL;DR: Stress-strain curves of 150 copper whiskers, whose thickness ranges from 4 to 30µ and growth orientations are parallel to the three principal crystallographic orientations, have been investigated by an Instron-type tensile machine at room temperature as discussed by the authors.
Abstract: Stress-strain curves of 150 copper whiskers, whose thickness ranges from 4 to 30µ and growth orientations are parallel to the three principal crystallographic orientations, have been investigated by an Instron-type tensile machine at room temperature. Thinner whiskers have shown characteristic sharp yield points. The upper yield stress of some thinner whiskers reaches nearly the theoretical strength of an ideal perfect crystal, but it decreases as the thickness increases. In the subsequent “easy glide” region, corresponding to the propagation of one or a few Luders bands, pronounced serrations appear, and both of flow stress and Luders strain vary approximately in inverse proportion to the thickness. The hardening rate in the most rapid hardening stage of the stress-strain curve increases with increasing thickness. In whiskers, thicker, than about 20µ, the sharp yield point and serrated “easy glide” region are scarcely observable, and their Stress-strain curves are similar to those of bulk crystals.
TL;DR: In this paper, a microhardness analysis of grain boundaries in irons of various purities, and in certain iron-base alloys, has been investigated by means of a micro-hardness technique.
Abstract: Hardening at the grain boundaries in irons of various purities, and in certain iron-base alloys, has been investigated by means of a microhardness technique. The difference between the grain-boundary and grain-interior hardness values (∆H) increased as the load applied to the indenter was decreased. Zero values of ∆H were found for loads > ∼ 14 g. Factors affecting the grain-boundary hardening were studied: (a) Additions of tungsten or molybdenum reduced the grain-boundary hardness to that of the grain interior at ∼ 0.5 at.-% solute; manganese additions did not affect ∆H (b) Quenching from 900°C eliminated the hardening effect in all the materials investigated. Annealing to equilibrium at temperatures between 300 and ∼ 750°C caused a return of the hardening, the magnitude of which was independent of the annealing temperature. (c) A kinetic study of the rate of recovery of the hardening effect, following quenching from 900°C, showed that it occurs very rapidly. The conditions required for the obser...
Patent•
19 Dec 1968
TL;DR: In this paper, a Boron-constrained additive additive material is used to cover the surface of SINTERED, CEMENTED-CARBIDE, and COBALTBONDED TUNGSTEN CARBIDE.
Abstract: SINTERED, CEMENTED-CARBIDE COMPOSITIONS, E.G. COBALTBONDED TUNGSTEN CARBIDE, ARE HARDENED BY PERMEATING A BORON-CONTAINING MATERIAL INTO SURFACE OF THE SINTERED COMPOSITION. THE BORONIZING TREATMENT CAN BE EFFECTED FOR EXAMPLE, BY HEATING THE COMPOSITION WITH A SOLID FORM OF THE BORON-CONTAINING MATERIAL, OR B ELECTROLYSIS IN A MOLTEN BORON SALT BATH.
TL;DR: In this paper, the critical resolved shear stress (CRSS), optical absorption spectrum and the lattice parameter were measured as a function of dose and post-irradiation annealing.
TL;DR: In this article, a critical analysis has been made of both the experimental evidence on the deformation characteristics of neutron irradiated copper crystals and the hardening models which have been proposed.
Abstract: A critical analysis has been made of both the experimental evidence on the deformation characteristics of neutron irradiated copper crystals and the hardening models which have been proposed. It is shown that the observed behaviour is explicable only in terms of the presence in as-irradiated crystals of a spectrum of thermally activated obstacles with values of F max of μb 2 and greater. During annealing the obstacles with the smallest values of F max are removed first, resulting in the formation of a low temperature ‘athermal’region in the flow stress–temperature curve with deformation characteristics similar to those observed in crystals containing very hard second-phase particles. The conclusion of Koppenaal and Arsenault (1965) that only a single type of thermally activated obstacle exists in irradiated copper is shown to be incorrect. Fleischer's (1962 b) theory, as applied to irradiation hardening, is criticized.
TL;DR: In this paper, the interdependencies of stress, strain rate and temperature during hot working and secondary creep are shown to be similar during steady state deformation at a constant temperature above 0.5Tm.
Abstract: 1.
During deformation at a constant temperature above 0.5Tm, there is a steady-state regime where both stress and strain rate remain constant independent of strain.
2.
The interdependence of stress, strain rate and temperature during steady-state hot working and secondary creep are similar.
3.
During the hardening stage, simultaneous dynamic recovery causes the dislocations to arrange into sub-boundaries.
4.
During the steady state, the balance between hardening and recovery maintains the dislocation density constant as subgrains of constant size and misorientation.
5.
The subgrains remain equiaxed, indicating that the sub-boundaries continuously break up and reform. It is proposed that this process inhibits recrystallization during high strain-rate deformation.
6.
The size of the subgrains and the neatness of their boundaries increase as the temperature increases and the strain rate decreases.
TL;DR: In this article, the effect of 2 Mev electron irradiation below 31°K on the yield stress of copper single crystals measured at 25°K was investigated and interpreted as dispersed barrier hardening due to interstitials.
Abstract: This paper reports the effect of 2 Mev electron irradiation below 31°K on the yield stress of copper single crystals measured at 25°K. Irradiation produces a large increase in the yield stress, which is interpreted as dispersed barrier hardening due to interstitials.
TL;DR: In this article, a theory is proposed to explain the dynamic plastic buckling of short cylindrical shells subjected to uniform radially inward impulses, and formulas are derived which predict wavelengths and threshold impulses in general agreement with the experimental results that are presented.
TL;DR: The effect of fast neutron irradiation on the rate controlling mechanism for slip in iron and dilute iron alloys has been investigated in this paper, where stress relaxation techniques have been used to determine the components of the applied stress and the activation volumes.
TL;DR: In this paper, the effects of temperature and strain rate changes on the yield stress have been used to analyse the strengthening produced in NaCl single crystals containing 675 mole p.p.m. Mn++.
Abstract: The effects of temperature and strain rate changes on the yield stress have been used to analyse the strengthening produced in NaCl single crystals containing 675 mole p.p.m. Mn++. The temperature dependence of the yield stress observed at low temperatures can be interpreted satisfactorily in terms of the thermally activated cutting of particles; the particles are considered to be trimers. The athermal yield stress can be explained in terms of contributions from precipitation hardening by the Orowan mechanism and from coherency stresses due to trimers.
Patent•
15 Jul 1968TL;DR: The results obtained were as follows: according to the results of electrical resistivity measurements, it would be possible in these experiments to get the solid solubility limit of Zr in Al up to about 1.2wt. as mentioned in this paper.
Abstract: The studies on recrystallization of Al-Zr alloys have been made by many investigators since Harrington's report in 1949. These studies showed that age hardening property was found in these alloys. However, the authors were interested with the further examination of this property in the above alloys containing much more solute of Zr. The property was investigated on super-saturated solutions obtained by quenching of uniform molten bath of Al-Zr alloys.The results obtained were as follows:(1) According to the results of electrical resistivity measurements, it would be possible in these experiments to get the solid solubility limit of Zr in Al up to about 1.2wt.% by quenching of molten Al-Zr alloys.(2) Age hardening of these alloys containing more than 0.4wt.% of Zr was remarkable and it increased to the maximum at about 1.2wt.%.(3) Precipitation of Zr took please at 300°C for 1hr. annealing and the maximum precipitation hardening was given at about 400-450°C.(4) Inpurities such as Fe, Si, etc. seemed to have deep effects on the precipitated structures of these alloys.
TL;DR: In this paper, annealing results showed that the magnitude of the increase in yield stress is at all times determined by the remaining defect concentration and that approximately 85% of the defect barriers, probably interstitials, anneals out in Stage I (below about 60°K).