Showing papers on "Hardening (metallurgy) published in 1980"

Measurement and Analysis of Plane-Strain Work Hardening

Abstract: A new technique for measurement of plane-strain work hardening has been developed which uses tensile loading and computer analysis for interpretation, and which eliminates the experimental uncertainties of large strain gradients, friction, and out-of-plane bending inherent in the usual plane-strain deformation modes. Plane-strain and tensile work-hardening curves have been measured for 2036-T4 aluminum alloy using several types of sheet specimens. The work-hardening rate in plane strain is lower than that in uniaxial tension. In each case a Voce-type empirical work hardening law represents the data well. Hill’s theories cannot account for these data because the isotropic hardening assumption is violated. A method of analysis was introduced to determine Hill’s newm parameter as a function of strain andm was found to vary from 1.6 to 2.0 in the strain range 0.02 ≤ e ≤ 0.18.

Surface hardening by particle injection into laser melted surface

Abstract: A method of impregnating the surface of a metal substrate with wear resist particles to impart wear resisting characteristics to the surface. The substrate surface is subjected to a relatively moving high-powered laser beam to cause localized surface melting in passes thereacross, and hard wear resistant particles are forcibly velocity injected into the melt. The particles are captured upon solidification of the melt pool and retained therein by metallurgical bond. A wear resistant layer is formed which is an integral part of the underlying material.

On the law of mixtures in dual-phase steels

Abstract: The applicability of the equation of the stress in the ferrite at the ultimate tensile strain to dual-phase steels obtained by heating 1010 and 1020 grades was tested. The law of mixtures describe the tensile strength of 1010 steels provided the dislocation hardening is included. The equation application to other dual phase systems may require modification to account for differences in metallurgical parameters. (FS)

Effects of hydrogen on the plastic properties of medium-Carbon steels

Abstract: The effect of hydrogen on the plastic deformation of pearlitic and spheroidized 1045 steels is examined. We find that hyrogen in the dissolved state invariably hardens 1045 steel. Luders band formation and propagation require greater applied stress, the slope of the stress-strain curve is increased, and the amount of plastic deformation over a given stress-time history is decreased by dissolved hydrogen. We find, however, that microvoids, the population of which at a given degree of strain is increased by hydrogen of themselves are a softening influence. Furthermore, because hydrogen at very high input activity has the additional effect of generating very large gas pressures within the microvoids, such hydrogen produces an apparent softening effect. Some prior results in the literature are considered, and a reasonably consistent rationalization is given of the results in terms of the effects here described. An attempt is made to relate the hardening and softening effects to dislocation behavior. It is argued that the increase by hydrogen of the number of microcavities by decohesion, the reduction of the Peierls barrier to dislocation motion observable only in iron of very high purity, and the reduction of cross slip of screw dislocations are all manifestations of the reduction by hydrogen of the cohesive force between metal atoms.

Precipitation phenomena in the Mg-31 at% Li-1 at% Al alloy

Abstract: Precipitation phenomena produced in the β-phase (b c c) of the Mg-31 at% Li-1 at%Al alloy subjected to different heat treatments have been studied by sensitive single-crystal X-ray diffraction techniques. The variation of the hardness values of specimens quenched and then aged was also examined. It was confirmed that AlLi is a stable phase at room temperature for the examined Al content; AlLi precipitation is only produced for very slow cooling rates from the β-field. Phase reactions for specimens quenched and then aged can be summarized as follows: β → β+θ+α after ageing at room temperature; β→ β+ θ+α+ AlLi after ageing at 473 K. A considerable increase of the hardness, which attains its maximum value after about 30 h ageing at room temperature, was observed. Neither the α-phase nor the AlLi-phase precipitation can account for the observed hardening process. The presence of the θ-metastable phase when the hardness reaches its maximum value is verified.

Creep and stress rupture of a mechanically alloyed oxide dispersion and precipitation strengthened nickel-base superalloy

Abstract: The creep and stress rupture behavior of a mechanically alloyed oxide dispersion strengthened (ODS) and γ′ precipitation strengthened nickel-base alloy (alloy MA 6000E) was studied at intermediate and elevated temperatures. At 760 °C, MA 6000E exhibits the high creep strength characteristic of nickel-base superalloys and at 1093 °C the creep strength is superior to other ODS nickel-base alloys. The stress dependence of the creep rate is very sharp at both test temperatures and the apparent creep activation energy measured around 760 °C is high, much larger in magnitude than the self-diffusion energy. Stress rupture in this large grain size material is transgranular and crystallographic cracking is observed. The rupture ductility is dependent on creep strain rate, but usually is low. These and accompanying microstructural results are discussed with respect to other ODS alloys and superalloys and the creep behavior is rationalized by invoking a recently-developed resisting stress model of creep in materials strengthened by second phase particles. The analysis indicates that at the intermediate temperature the creep strength is controlled by the high volume fraction of γ′ precipitates and the contribution to the creep strength from the oxide dispersion is small. At the elevated temperature, the creep strength is derived mainly from the inert oxide dispersoids.

The effect of prior deformation on spinodal age hardening in Cu-15 Ni-8 Sn alloy

Abstract: The structure and kinetics of aged Cu-15 Ni-8 Sn with and without prior deformation was investigated by means of X-ray diffraction and transmission electron microscopy. Deformation prior to aging is known to accelerate the hardening process in this alloy. The purpose of the study was to determine whether the strengthing mechanisms are kinetically enhanced through modified alloy decomposition or through other mechanisms. Deformation does not affect most of the features of structure development, including DO22 ordering in the tin-rich phase. However, for a given aging treatment, cold worked material shows a reduced strain modulation. The accelerated strengthening response in cold worked alloys cannot be attributed to an accelerated or altered decomposition process. It is suggested that the coarsened spinodal structure and the dislocation structure interact in a synergistic way to give the observed strengthening acceleration.

Mechanical Properties of Fine‐Grained Magnesium Oxide at Large Compressive Strains

Abstract: Fine-grained polycrystalline MgO specimens were deformed in compression at constant strain rates of ∼6.7×10−6 s−1 to 6.7×10−5 s−1 at 1173 to 1423 K. Both mechanical data and microstructural observations are distinctive of a diffusion-accommodated flow, where the grain-size parameter is of prime importance in enhancing plasticity. Under suitable experimental conditions, superplastic strain was achieved in specimens; no change was detected in the equiaxed-grain shape configuration. Finally, the effect of grain growth during deformation was considered; specimens of initial grain size ∼0.1 μm showed an apparent hardening which was quasi-linear with time.

High strain fatigue of a type 316 stainless steel

Abstract: — High strain fatigue tests of Type 316 stainless steel have been carried out at room temperature and 600°C. Cold work reduces the life relative to the annealed condition when considered in terms of plastic strain per cycle but not when the total strain range is used. It also renders the material far more resistant to cyclically induced changes in strength than the annealed state in which the strength is more than doubled at 600°C. Strain ageing causes further instability and enhances the hardening and loss of ductility in the annealed material. Because of the large number of variables involved, comparison with other work is unable to identify the parameters most influential in determining endurance. It is argued that where a fatigue–creep interaction occurs, then cyclic hardening will promote a higher creep resistance in a sequential interaction and favour a fatigue dominated failure in a simultaneous interaction.

Age-hardening of Dental Ag-Pd-Cu-Au Alloys

Abstract: Age-hardening mechanisms of dental Ag-Pd-Cu-Au alloys were investigated by means of electron microscopic observations. Hardening was due to the precipitation of the L1o type CuPd-ordered platelet in the grain interior and to the discontinuous precipitation at the grain boundary. The characteristics of age-hardening curves were determined by rates of continuous and discontinuous precipitation.

Manufacturing of flexible abrasives

Abstract: Abrasive grains are bound to a flexible support by a pattern of resin applied by means of a curved stencil having a wall thickness of 0.08 to 1 mm and having holes with a diameter of 0.05 to 3 mm, the total hole area amounting to 5 to 50% of the area of the stencil. A top binding agent is applied before or after the drying or hardening of the resin.

Dislocation theories of work hardening and yield surfaces of single crystals

Abstract: The nature of existing dislocation hardening mechanisms are analyzed. This analysis shows that the hardening mechanisms can be classified into two categories: isotropic and kinematic; consequently a general physical hardening law, which incorporates the concept of the degree of isotropy in work hardening, is proposed. The corresponding motions of yield surface in both stress and strain space are examined on the basis of this general hardening law and its two extreme cases: isotropic and kinematic hardening.

Fatigue softening and hardening in mild steel detected from Barkhausen noise

Abstract: The measurement of Barkhausen noise is used to follow the fatigue process in a mild steel. The variation in the root-mean-square (rms) value of the noise with bending stress during single-strain cycles and in unloaded samples is determined at several stages of fatigue life. The fatigue softening and hardening are found to be sensitively revealed by specific changes in the shape and area of the noise versus stress loops and also in the variation in the noise in unloaded samples, corresponding to changes in the residual stress state. The high sensitivity of the magnetic measurement technique is emphasized.

Large wire drawing plastic deformation in aluminum and its dilute alloys

Abstract: The microstructures and hardening characteristics of Al and Al with dilute additions of soluble and insoluble impurities were compared during wire drawing at room temperature to true strains (e w ) of 4.95. Three stages of microstructure change are observed: formation of a dislocation cell structure; cell boundary sharpening and cell size refinement; dynamic recrystallization. A minimum effective cell size is reached at an intermediate strain level corresponding approximately to the onset of dynamic recrystallization. The amounts and types of impurities at levels less than 1 pct have a great effect on the details of the microstructural changes as well as the hardening characteristics. 99.98 pct pure Al alternately saturates and hardens frome w = 0 to 4.95. Al-0.6 Fe (insoluble) work softens neare w = 3.5. Al-0.2 Mg (soluble) and EC Al (with 0.15 pct soluble and insoluble impurities) both work harden at a diminishing rate toe w ≃1.25 then enter a linear hardening stage which persists toe w ≃5. A linear relation between yield strength and inverse cell size is established for EC Al and Al-0.2 Mg in the cell refinement strain range; however, the Petch slope is much less than that of similar Al alloys subjected to elevated temperature dynamic or static recovery. Al-0.6 Fe does not exhibit a consistent linear relation between yield strength and inverse cell size. These differences can be attributed to the degree of recovery and the interrelation between cell size, cell boundary character and total dislocation density.

Cyclic wear behavior (fretting) of a tempered martensite steel

Abstract: Cyclic wear experiments were conducted on a 4130 steel with a tempered martensitic structure in laboratory air and in flowing argon. Temperatures of the sliding interfaces were measured and were of the order of + 10 K above the ambient. The interface temperatures were observed to be cyclic and correlated with maxima in sliding velocities between the surfaces. Microhardness measurements and optical and electron metallographic observations of fretted surfaces indicated selective surface hardening and the formation of large numbers of thin metallic flakes. The thickness of the flakes corresponded to the thickness of the hardened layer and were formed from subsurface crack initiation processes. The results of this investigation do not support many previously proposed models for fretting damage. Rather a micromechanical cracking model is proposed which appears to explain observed results in terms of a delamination model.

Substructure and strengthening mechanisms in 2.25 Cr-1 Mo steel at elevated temperatures

Abstract: The substructures of thermally aged, creep deformed and fatigued 2.25 Cr-1 Mo steel have been studied using optical and transmission electron microscopy. In agreement with earlier work, the substructure of the proeutectoid ferrite was found to be very stable when exposed to thermal aging or creep deformation. This stability is explained based on the tendency of molybdenum atoms to form pairs in the ferrite matrix. Nucleation and growth of additional carbide particles during creep testing was not observed. The results of these creep tests and those of Klueh have been interpreted on the basis of Mo pair stability and the affinity between molybdenum and carbon. Fatigue tests at 866 K, however, did produce a fine Mou2C precipitate which contributed to secondary cyclic hardening in tests lasting longer than 200 h. The alloy was found to undergo early cyclic hardening followed by abrupt softening within the first tens of cycles.

Method of manufacturing cement products having superior mechanical strength

Abstract: This invention is based on the discovery by the inventors that, if a preliminary hydration hardening process and a full-scale hydration hardening process are provided after the molding process, and a process for burning a hardened body of cement at a high temperature is provided between the preliminary and full-scale hardening processes, it is possible to obtain a molded product of cement having a higher mechanical strength than any such product according to any known method including no such burning process. According to this invention, there is provided a method of manufacturing a product of cement having high mechanical strength, which method comprises the steps in sequence of adding water, and if required, glass fibers or other reinforcing material, into a mixture of cement and an aggregate, and kneading the whole completely; molding the kneaded mixture into a desired shape; hardening the molded body preliminarily by hydration; burning the preliminarily hardened body at a high temperature; and hardening the burned body on a full scale by hydration.

Constitutive Relations for the Non Elastic Deformation of Polycrystalline Ice

Abstract: Constitutive relations for the non-elastic deformation of polycrystalline ice are proposed. Two types of hardening are introduced (isotropic and kinematic hardening). These case variables evolve by defined laws and are affected by two counteracting processes: strainhardening and softening. All the transient behaviour is described by this model. Quantitative predictions are compared with the corresponding experimental data for creep recovery tests.

The hardening of middle east petroleum asphalts in pavement surfacings

Abstract: The paper examines the long term service performance of the bituminous binder-aggregate composites. If the composite has been well designed, if the construction is adequate, and if the aggregate used is durable and has acceptable resistance, then the life of the surfacings will mostly depend on the performance of the binder. The focus of this study is the hardening of the bitumen binders that have been almost wholly derived from Middle East crude petroleums. These binders have been used in pavement surfacings in Australia for the last 15 years. The study reviewed the following specifics: mechanism of hardening; relationship between level of hardening and surface distress; properties of the hardening bitumens; development of a laboratory test to predict hardening in service; relationship between bitumen hardening in sprayed seals and durability test results; relationship between bitumen hardening in a thin dense hot mix surfacing and durability test result; and, methods for improving the resistance of bitumens to hardening in service.