Modeling solid solution strengthening in nickel alloys

The yield stress of multicomponent nickel solid solution alloys has not been modeled in the past with respect to the effects of composition and temperature. There have been investigations of the effect on the yield stress of solutes in binary systems at a fixed temperature, but the effects on the yield stress of multiple solute elements and temperature changes have not been investigated. In this article, two different forms of the trough model are considered for nickel-base alloys to determine the most applicable model for solid solution strengthening in the system. The yield stresses of three binary nickel-chromium and three ternary nickel alloys were determined at a range of temperatures. The yield stress of the alloys was then modeled using the Feltham equation. The constants determined in fitting the Feltham equation to the experimental data were then applied to other experimental solid solution alloys and also to published information on commercial solid solution nickel alloys. It was found that the yield stress of the nickel solid solution alloys could be modeled successfully using the Feltham equation.     

Structure and Properties of Cast Near-Congruent Copper-Manganese Alloys

Microstructure development in the casting of copper-manganese alloys based on the congruent point at 34.6 wt pct Mn and 1146 K (873 °C) has been studied. The alloys were prepared by induction melting of electrolytic Cu and Mn in clay-graphite crucibles in open air. Under conventional casting conditions, the alloys exhibit fine cellular (non-dendritic) solidification morphology with a distinct absence of solidification shrinkage microporosity, and they maintain these attributes over a composition range of approximately 3 wt pct Mn about the congruent point. The high Mn concentration in the alloy admits carbon into solution in the melt, resulting in formation of manganese carbide Mn₇C₃ particles having two different forms (globular and angular) in the cast microstructure. The Mn carbide was eliminated or controlled to low levels by melting in an alumina or a silicon carbide crucible, or in a clay-graphite crucible at lower temperatures. Microstructure development in casting the alloy was analyzed in terms of the available phase diagrams and thermochemical data. Hardness and tensile testing indicated a potent solid solution strengthening effect of Mn and high ductility in the as-cast condition, with additional hardness (strength) when the alloy contains the Mn carbide phase.     

Solid Solution strengthening of high purity niobium alloys

Athermal solid solution strengthening was examined in substitutional Nb(Cb)-Hf, Nb-W, and Nb-Ta alloys deformed at 900 K. Ultrahigh vacuum degassed single crystals were tested in compression. The concentration dependence of the yield stress is nearly linear in Nb-Hf and Nb-W alloys for the range of compositions tested (< 6 at. pct). The rate of hardening with solute addition was the greatest for the Nb-Hf alloys, considerably less for the Nb-W alloys, and the least for the Nb-Ta alloys which exhibited little strengthening. The results indicate that athermal strengthening in these alloys appears to be primarily dependent on the atomic size misfit between solvent and solute atoms and not on the elastic modulus mis-fit. Results on the slip behavior are also presented. J. R. SLINING, formerly Research Assistant, Department of Metal-lurgical Engineering, Michigan Technological University, Houghton, Mich. 49931     

镍元素对18K金固溶强化的影响

采用氧气乙炔火枪制备了4种镍质量分数分别为0,2.5,5,8%的18K金合金;利用显微硬度仪和X射线衍射仪研究了镍质量分数对18K金固溶强化的影响。其研究结果表明:随着镍质量分数的增加,合金的硬度不断增加;这主要是由于镍质量分数的增加提高了合金的固溶度,加强了固溶强化机制。此外,镍元素对金的固溶强化效果要强于其他补口元素,这也是合金硬度提高的原因。     

Effect of scandium on the phase composition and mechanical properties of ABM alloys

The effect of scandium on the composition and mechanical properties of ABM-1 alloys (Al-30% Be-5% Mg) is studied. The scandium content is varied from 0.1 to 0.5 wt %. It is established that, in the studied part of the Al-Be-Mg-Sc system, an aluminum solid solution (Al) and the ScBe₁₃ compound are in equilibrium with a beryllium solid solution (Be). Magnesium dissolves in both the aluminum component and the ScBe₁₃ compound. The strengthening effect related to the decomposition of the solid solution and the precipitation of Al₃Sc cannot be extended to the strengthening of ABM-type alloys. Additions of 0.1–0.15 wt % Sc only weakly improve the mechanical properties of the alloys due to the refinement of beryllium-component grains. At high scandium contents, the strength increases insignificantly due to primary precipitation of ScBe₁₃ and the plasticity decreases simultaneously.     

层错能对高能球磨铜合金的影响

试验中以球磨的方法制备了一系列不同成份的Cu—Zn及Cu—Al合金（层错能〈75MJ／m^2）。对Zn和Al的固溶强化效果及其降低铜合金层错能的作用进行了研究。实验结果显示,随着Zn或Al含量的升高,（试样的）显微硬度（HV）值增加,符合固溶强化的规律。在相近原子百分比的条件下比较Cu—Zn和Cu—Al合金的HV值,显示当合金中无第二相出现时,Zn的固溶强化效果优于Al;另一方面,随着Zn％及Al％（原子百分比）的增加,Cu～Zn及Cu—Al合金的层错能下降,而层错能的降低导致了强化的产生,这种情况下Zn和Al的不同强,L化效果可以用公式k=Gb/2π（1-v）（a-δ·FE）^[1]来评价,式中K是Hall—Petch关系的斜率。评价的结果与实验数据（合金的显微硬度值）是相吻合的。     

A study of work hardening in austenitic FeMnC and FeMnAlC alloys

Two austenitic FeMnAlC alloys with aluminium contents of 0 and 2.7 wt% were strained in tension between 193 and 823 K. Serrated stress-strain curves, inverse strain-rate dependence of flow stress, and high work hardening exhibited in particular temperature ranges for both alloys were characteristic of dynamic strain aging. The apparent activation energy for the onset of serration increased from 14.4 to 22.3 kcal/mol due to the addition of 2.7 wt% Al. It was found that the high work-hardening rate cannot be attributed to strain-induced deformation twinning when serrated stress-strain curves occurred. From the evidence of the present study and the known effect of aluminium on the diffusivity and activity of carbon in austenitic high-manganese steel, it is suggested that dynamic strain aging is the major cause of work hardening within the intermediate temperature range from 298 to 493 K for 0 wt% Al and 393 to 593 K for 2.7 wt% Al in the present austenitic FeMnAlC alloys.     

Study of the phase equilibria and the decomposition of a supersaturated solid solution in magnesium alloys with aluminum, calcium, and manganese

Magnesium alloys Mg-Al-Ca-Mn having 1 wt % Al, up to 1.8 wt % Mn, and up to 1.6 wt % Ca are studied by optical microscopy, electron microprobe analysis, and electrical resistivity and microhardness measurements. The phase equilibria corresponding to the Al, Ca, and Mn concentration ranges under study were determined and sections of the isothermal tetrahedrons of the Mg-Al-Ca-Mn phase diagram in the Mn-rich region at 450 and 300°C have been constructed. As was found, manganese does not affect the decomposition kinetics of the magnesium supersaturated solid solution in ternary Mg-Al-Ca alloys but increases their hardness.     

Synthesis and Characterization of Novel Chromium-Free Nickel Alloy Electrode Materials

The synthesis of two Cr-free nickel-based alloys designated as 1S with 6.5 pct Mn and 2H without Mn of compositions varying between 40 to 43.5Ni, 20Mo, 22 to 25Fe, 10Cu, 6.5 to 0Mn, 1Ti, and 0.5Al (wt pct) as filler materials for TIG welding application was performed. New filler materials were developed to reduce carcinogenic hexavalent chromium (Cr⁶⁺) fumes generated during the welding of 300 series austenitic stainless steel. The Cr-free nickel alloys were characterized for microstructure and mechanical properties. The developed alloys showed good microstructure stability in as-cast and solution-treated conditions. A material properties simulation software JMatPro predicted that 2H alloy has 2 wt pct more γ (solid solution) phase than in 1S but has 2.2 wt pct less γ′ (strengthening precipitates) phase than in 1S alloy. The tensile strength of 1S alloy was about 2.2 pct more than 2H. The solution treatment of both alloys decreased the hardness, tensile and yield strengths by about 21 pct but ductility improved by about 17 pct. Fracture studies of both alloys showed the ductile mode of failure.     

间隙原子对高熵合金组织及性能影响的研究现状

高熵合金作为一种新型的合金体系,虽然其组成元素复杂,但能形成简单的固溶体,具有许多异于传统合金的结构和性能特征,其研究近年来成为热点。间隙原子可以溶入基体晶格间隙产生固溶强化,与合金元素结合形成细小弥散强化相,以及降低层错能,改变位错运动方式等,从而改善高熵合金性能。文章在论述高熵合金组织结构特性的基础上,分析了间隙原子C、N、O、B对高熵合金相形成规律、强化机理、塑性变形机制的影响,总结了间隙原子含量及其产生的固溶强化、晶粒细化、第二相强化作用对高熵合金组织性能等方面影响的研究进展,最后提出了含间隙原子的高强高韧高熵合金组织结构设计研究的新方向。      

The effect of microstructure and composition on the properties of vapour quenched AlCr alloys—II. Tensile properties

The effect of chromium and iron additions and of annealing and working on the microstructure and tensile properties of vapour quenched AlCr and AlCrFe alloys has been determined. Tensile strengths of the worked AlCrFe alloys were in the range 568–831 MPa. Chromium in solid solution or iron present as iron-rich precipitates increased the yield stress by 44.7 MPa/at.%Cr and 333 MPa/at.%Fe respectively. The contributions to the yield strength of AlCr alloys were solid solution 40% and dislocation density/cell size 60% and to the yield strength of AlCrFe alloys were solid solution 25%, iron-rich precipitates 42% and dislocation density/cell size 33%. Vapour quenching may allow the more efficient use of alloying elements in the strengthening of Al-alloys and greater flexibility in obtaining the desired combination of solute concentration, particle volume fraction and particle size.     

Magnesium-rich Mg-Al2Ca alloys

The magnesium solid solution in the Mg-Al-Ca system is confirmed to be in equilibrium with the Al₂Ca phase of the Al-Ca system. The solubility of Al₂Ca in solid magnesium is determined, and its decrease with decreasing temperature suggests the decomposition of a supersaturated solid solution in Mg-Al₂Ca alloys. The decomposition kinetics of the supersaturated solid solution and the accompanying strengthening effect in the alloys at aging temperatures of 175 and 200°C are established.     

Thermal stability of invar FeNi alloys above 500°C

The high-temperature thermal stability of three FeNi alloys (with 35.0, 40.1 or 43.8 at. % Ni) was investigated by aging samples for 230 days at 625°C. Anomalous small-angle X-ray scattering, analytical transmission electron-microscopy and magneto-thermogravimetric Curie temperature measurements were used for this purpose. The wave-length dependence of the anomalous scattering effect was found to be opposite to what would be expected from a decomposed solid solution. The absence of concentration fluctuations was further confirmed by the other two techniques. Taking into account previous aging results, it is concluded that, in the investigated composition range, FeNi alloys are thermally stable above 500°C.     

Deformation of Nb-W single crystals: Athermal solid solution strengthening

The athermal component of the flow stress of single crystals of niobium and four substitutional solid solution strengthened Nb-W alloys (1, 3, 6, and 15 at. pct) has been measured. The magnitude of the athermal stress was obtained by the method utilizing the temperature dependence of the flow stress and by a stress relaxation method. The agreement between these two methods is good. Athermal strengthening is a linear function of concentration over most of the composition range. No current athermal hardening theory is completely consistent with the experimental results. Formerly with the Advanced Materials Research and Development Laboratory, Pratt and Whitney Aircraft, Middletown, Conn.,     

Solid solution softening and strain-rate sensitivity of Fe-Re and Fe-Mo alloys

The resolved shear stress and strain-rate sensitivity of Fe-Mo and Fe-Re alloys, well within the solid solution range, were measured versus temperature and compared with previous results for Fe-Ti alloys. The strain-rate sensitivity-temperature curves shifted systematically to lower temperatures as solute was added. The resolved shear stress was divided into two parts, a dynamic part which is a function of strain-rate and a static part which is not. The strain-rate sensitivity data were inverted to give the dynamic part of the flow stress and this was subtracted from the resolved shear stress to give the static part of the flow stress. Significant solid solution softening occurred in the dynamic part of the flow stress at 166 and 196 K. This is due to intrinsic effects and not to scavenging of im-purities. The static part of the flow stress is made up of two parts, a peaking effect super-imposed on normal solid solution hardening.     

Conditions for growth of extended Al-rich Al-Mn alloy solid solutions and Al-Al6Mn eutectic during rapid solidification

Al-Mn alloys containing between 1.3 and 5.6 wt% Mn have been rapidly solidified by a modification of the Bridgman crystal growing technique at growth velocity V between 0.1 and 2 mm/s and a temperature gradient of 10 K/mm. Growth temperatures of the unextended and extended αAl solid solutions in the alloys respectively containing 1.3 and 2.1 wt% Mn, and of the extended Al-Al₆Mn eutectic containing 3.2 wt% Mn, have been measured as a function of V by interpreting the output of a sheathed thermocouple immersed in the melt and travelling with it during unidirectional solidification. These measurements of tip temperature as a function V for the Al-2.1 wt% Mn alloy are the first to be reported for a solid solution extended by rapid solidification. The measurements of tip temperature and concentration for both unextended and extended αAl solid solutions are in good agreement with predictions of a development by Kurz, Giovanola and Trivedi of Kurz and Fisher's model of dendritic growth. Corresponding measurements of growth temperature and eutectic spacing as a function of V for the extended Al-Al₆Mn eutectic containing 3.2 wt% Mn suggest that its growth is occurring at somewhat higher undercooling and larger spacing than predicted for growth at the extremum.     

Strengthening by ordered precipitates in a Ni−Ni4Mo system

The strength characteristics and microstructures of aged Ni−Mo alloys containing ordered (Ni₄Mo) precipitates were studied as a function of aging time and temperature. It was found that 17 at. pct Mo alloy aged at 750°C produced a uniform dispersion of cuboidal β precipitates which coarsened with time producing a gradual increase in flow stress. The flow stress increment was found to vary in qualitative agreement with both order strengthening and coherency strain models. Both these models give over-estimates of the strengthening increment. A negative dependence of flow stress on temperature is attributed to coherency strain contributions.     

Effect of dissolved tungsten on the deformation of 70Ni-30Fe alloys

A series of Ni-Fe alloys containing various levels of tungsten in solid solution have been prepared as a means to assess the influence of solid solution strengthening on the mechanical behavior of monolithic 70Ni-30Fe. In particular, 70Ni-30Fe alloys plus equilibrium concentrations of tungsten in solid solution nominally correspond to the compositions associated with the matrix-only portion of certain tungsten heavy alloys, that is, alloys comprised of a high volume fraction of nominally pure tungsten particles embedded within a minority Ni-Fe-W based matrix. The study shows that the working solubility of tungsten within the 70Ni-30Fe base composition increases slightly with temperature, from approximately 21 wt pct at room temperature to approximately 23 wt pct at 1400 °C. Increasing the level of tungsten in solid solution leads to increases in room-temperature yield strength, tensile strength, and ductility. In contrast, the deformation characteristics of the alloys, as quantified by the power-law work-hardening exponent, n, and the strain-rate-sensitivity exponent, m, show little variation with tungsten solute concentration.     

effects of hydrogen on low temperature hardening and embrittlement of V-Cr alloys

The effects of H on the strength and ductility of V-Cr alloys were investigated from 78 to 300 K. Alloy softening which was observed at low temperatures for a V-2.5Cr alloy was mitigated by the addition of H. Hydrogen embrittlement, as measured by reduction of area, was observed in both hydride forming and nonhydride forming alloys. Analysis of the strengthening in hydrogenated V-Cr alloys showed that the predominate effect of H was to increase the thermally activated component of the yield stress. Comparison of the solid solution hardening effect caused by Cr or Ti in V showed that Ti produces greater strengthening, atom for atom, than does Cr, but that the difference cannot be explained solely by larger size and modulus misfits of solute and solvent atoms.