Solution-treated Specimens Research Articles

Damping properties on age hardening of Al–7Si–0.3Mg alloy during T6 treatment

The present study aimed to investigate the effect of age hardening on variation of damping capacity with tensile properties of Al–7Si–0.3Mg aluminum alloy. As an index of damping capacity, the specific damping capacity was chosen and obtained from conversion with logarithmic decrement on fluctuation decay curve by cantilever beam type excitation. The T6 treatment condition for maximum specific damping capacity (SDC) is coincided with the maximum age hardening condition by formation of GP zone (Mg 2Si), but it is simultaneously decreased with overaging. Although the SDC of solution-treated specimen decreased with solutionizing time, the SDC at peak aging condition increases with solutionizing time. The damping behavior of Al–7Si–0.3Mg alloy during age hardening was influenced remarkably upon the dislocation damping mechanism based on the Granato–Lücke theory.

Age hardening by dendrite growth in a low-gold dental casting alloy

Commercial low-gold dental casting alloy composed of Ag–Pd–In–Au–Zn was studied to clarify the age-hardening mechanism and related microstructural changes. The hardness of solution-treated specimen began to increase and reached the maximum value with ageing time, and then the maximum hardness value decreased by further ageing. The changes of X-ray diffraction (XRD) pattern during isothermal ageing revealed that the age hardening was not caused by phase transformation. By comparing the age-hardening curve with the changes in full-width at half-maximum of the XRD peaks at each ageing time, it was revealed that the coherency strains were formed in the Ag-rich matrix, which contributed to the hardness increase during ageing. From scanning electron microscopic observation and electron probe microanalysis, it was clarified that fine particle-like structures composed of InPd containing small amount of Zn gathered by diffusion in the Ag-rich matrix, and the coherency strains which formed during that time caused the hardness increase in the early stage of age-hardening process. The coherency strains were released by the progress of coarsening of Zn-containing InPd dendrite during further ageing, which caused the overaging in the later stage of age-hardening process.

The electrochemical behavior of austenitic stainless steel with different degrees of sensitization in the transpassive potential region in 1 M H 2SO 4 containing chloride

This paper investigates electrochemical methods to estimate the degree of sensitization (DOS) for as-rolled and solution-treated austenitic stainless steels (AISI 304). The change in DOS was introduced by heat treatment of various time periods at 700 °C, and the electrochemical experiments were conducted at 27 °C in 1 M H 2SO 4 + 0.2 wt.% NaCl. The results show that there is no obvious difference in the anodic polarization curves of the specimens with the differences in DOS. However, the DOS of specimens can be clearly differentiated with AC impedance response in a particular transpassive potential region. In the transpassive potential region of the anodic polarization curve, as overpotential is increased beyond the breakdown potential, three types of anodic dissolution, passive dissolution, grain-boundary attack, and pitting can be characterized. The DOS can only be correctly evaluated with AC impedance response in the middle of the transpassive potential region, where anodic dissolution is of grain-boundary attack type, from 1.05 to 1.1 V. The chromium-depleted zone was preferentially attacked and an intergranular corrosion was found for the serious sensitized specimen after AC impedance test. The healing effect was observed in as-rolled specimens as the specimens were heated more than 72 h, but the effect was not found in the solution-treated specimens sensitized for up to 480 h at 700 °C.

Influence of stabilization treatment on low cycle fatigue behavior of Ti alloy IMI 834

Low cycle fatigue (LCF) behavior of the near-α titanium alloy Ti-6Al-4Sn-4Zr-0.70Nb-0.50Mo-0.40Si (IMI 834) was studied at three total strain amplitudes (±0.8%, ±1%, and ±1.25%) at room temperature in both unstabilized and stabilized conditions. Specimens were solution treated in the (α+β) phase field at 1020 °C and quenched in water or cooled in air. The solution-treated specimens were stabilized by aging at 700 °C for 2 h, followed by cooling in air. Cyclic softening was exhibited both by the unstabilized and the stabilized specimens at all three strain amplitudes. However, the degree of softening was relatively greater in the stabilized specimens. The LCF life of the stabilized specimens was found to be much lower than that of the unstabilized specimen. This is attributed to the detrimental influence of the Ti 3Al precipitates present in the stabilized specimens.

Fabrication of composition-controlled TiNi shape memory wire using combustion synthesis process and the influence of Ni content on phase transformation behavior

TiNi intermetallic compounds were manufactured on an industrial scale using a combustion synthesis process that exploits the heat of formation between Ti and Ni. In this paper we investigate the influence of Ni content on the phase transformation temperature. The TiNi shape memory intermetallic compounds manufactured are homogeneous, show no gravity segregation, and have low oxygen content. Hot and cold plastic working can be carried out without difficulty. The martensitic (Ms) transformation temperatures of specimens that were solution-treated and heat-treated for aging fall rapidly with increased Ni content. However, the transformation temperature bottoms out at 51.4 at.% Ni and begins to rise again at 51.7 at.% Ni. The reason why the Ms temperature, etc., of the specimens heat-treated for aging rise more than for solution-treated specimens is that the Ti3Ni4 precipitates, causing the Ni content of the matrix to fall. The pattern of change in transformation temperature as a function of Ni content in the present experiment agrees with other researchers’ data in spite of the combustion synthesis process fundamentally different from the conventional melting process.© 2003 Elsevier Ltd. All rights reserved.

Cavitation erosion resistance of heat-treated NiTi

NiTi (Ti–50.8 at.% Ni) specimens were solution-treated at 1000 °C, followed by aging between 200 and 600 °C. The cavitation erosion resistance of all the aged specimens in deionized water was improved relative to the solution-treated specimen, with a maximum increase of about 8.7 times, which was achieved by aging at 500 °C. The results also indicate that both austenite and martensite contribute to the high cavitation erosion resistance of NiTi. It is also shown that a simple macro-indentation test employing a Rockwell indenter may be used for preliminary screening of heat-treated NiTi with respect to cavitation erosion resistance.

Evaluation of thermal aging embrittlement of austenitic stainless steels JN1, JJ1, and JK2 by cryogenic small-punch testing

Small-punch tests were conducted at 4, 77, and 293 K on three newly developed cryogenic austenitic stainless steels, JN1, JJ1, and JK2, which were solution treated, water-quenched, and then aged at 923, 973, 1023, and 1073 K for 5 h. Small-punch test energy was employed for the evaluation of the aging-induced embrittlement behavior in these materials. An SEM analysis of the fracture surface for the solution-treated steel specimens indicated a ductile fracture, having the highest SP test energy values. On the contrary, intergranular brittle fracture was observed in aged specimens. The small-punch test energy of materials decreased significantly as the aging process progressed. The highest and lowest decrease in small-punch test energy with aging temperature occurred in JN1 and JK2 steels, respectively. The decrease in small-punch test energy was shown to follow appropriately the aging-induced embrittlement in these materials. The difference in aging-induced embrittlement behavior for these steels was explained on the basis of the volume fraction of intergranular precipitates in aged samples.

On carbide dissolution in an as-cast ASTM F-75 alloy.

The solution treatment of an as-cast ASTM F-75 alloy was investigated. Microstructural evolution was followed during thermal processing, in particular with regard to the content and type of carbides formed. To evidence any probable carbide transformations occurring during the heating stage, as well as to clarify their effect on the carbide dissolution kinetics, three heating rates were studied. Image analysis and scanning electron microscopy techniques were used for microstructural characterization. For the identification of precipitates, these were electrolytically extracted from the matrix and then analyzed by X-ray diffraction. It was found that the precipitates in the as-cast alloy were constituted by both a M(23)C(6) carbide and a sigma intermetallic phase. The M(23)C(6) carbide was the only phase identified in solution-treated specimens, regardless of the heating rate employed, which indicated that this carbide dissolved directly into the matrix without being transformed first into an M(6)C carbide, as reported in the literature. It was found that the kinetics of dissolution for the M(23)C(6) carbide decreased progressively during the solution treatment, and that it was sensitive to the heating rate, decreasing whenever the latter was decreased. Because the M(23)C(6) carbide was not observed to suffer a phase transformation prior to its dissolution into the matrix, the effect of the heating rate was associated to the morphological change occurred as the specimens were heated. The occurrence of the observed phases was analyzed with the aid of phase diagrams computed for the system Co-Cr-Mo-C.

Qualitative model for creep of AZ91D magnesium alloy

Creep properties of specimens taken from the core of AZ91D magnesium alloy ingots (9 pct Al, 1 pct Zn) were examined in the temperature range of 120 °C to 180 °C and stress range of 40 to 115 MPa. Solution-treated and aged creep specimens were also tested. The creep rates observed were about three orders of magnitude lower than those of pure magnesium, and elongations to fracture were seen to be at least twice those of pure magnesium. A minimum creep rate was reached after approximately 2/3 of the creep life of the specimens (except for the aged specimens, in which the minimum creep rate appears at the beginning of the test). A qualitative model for the creep process in proposed on the basis of the creep tests and optical, scanning electron, and transmission electron microscopy. This model proposes that dislocation motion on additional slip systems is the primary creep mechanism and that cracking acts as a stress relief mechanism. Structural instability dictates the amount of hardening and, hence, creep resistance.

３００級１８Ｎｉマルエージング鋼の疲労特性に及ぼす時効条件および逆変態オーステナイトの影響

The influence of aging condition on fatigue strength of the 300 grade 18Ni maraging steel has been investigated in relation to the behavior of age hardening and the formation of reversion austenite. In this study, rotating bending fatigue tests were performed for three series of specimens with different aging condition; as solution-treated without aging, aged for various time at 753K which is the temperature applied for the industrial aging treatment, and overaged to form a small amount of reversion austenite. Effect of reversion austenite on fatigue strength was examined using specimens with the same static strength which had been controlled by varying aging temperature and time, namely under-aging or over-aging. The main results obtained are as follows.(1) In the case of 753K aging, the fatigue limits of specimens aged for 11ks to 48ks were nearly the same value, although an under-aged (2.8ks) specimen has as much lower value as a solution-treated specimen without aging treatment.(2) A small amount of reversion austenite is effective for increasing fatigue resistance. For instance, 2vol% of austenite was enough for improving fatigue limit of the maraging steel used, from 580MPa to 640MPa at the same hardness level of Hv 610.

Effect of solution and modification treatments on the crack propagation behaviour of Al-7Si alloy under resonant vibration

In order to investigate the influence of solution treatment and modification treatment on the crack propagation behaviour of A1-7Si alloy under resonant vibration, the unmodified and Sr-modified materials were tested. The experimental results indicate that the resistance to crack propagation is improved after solution treatment for both the unmodified and modified alloys. The improvement of cracking resistance of unmodified alloy is due to the change in the cracking paths from broken-through particles to particle/matrix interfaces. The unmodified alloy possesses better cracking resistance than does the modified alloy after solution treating at 535°C for 2 hours. On the other hand, the modification treatment shows no obvious improvement to cracking resistance. In the modified alloy, the crack paths of the as-cast and solution-treated specimens both preferentially progress toward the interdendritic zones. The as-cast alloy shows this trend more strongly and hence its cracking trajectory is more meandering and branching.

Microstructural evolution in a 17-4 PH stainless steel after aging at 400 °C

The microstructure of 17-4 PH stainless steel at various stages of heat treatment, i.e., after solution heat treatment, tempering at 580 °C, and long-term aging at 400 °C, have been studied by atom probe field ion microscopy (APFIM) and transmission electron microscopy (TEM). The solution-treated specimen consists largely of martensite with a small fraction of δ-ferrite. No precipitates are present in the martensite phase, while spherical fcc-Cu particles are present in the δ-ferrite. After tempering for 4 hours at 580 °C, coherent Cu particles precipitate in the martensite phase. At this stage, the Cr concentration in the martensite phase is still uniform. After 5000 hours aging at 400 °C, the martensite spinodaly decomposes into Fe-rich α and Cr-enriched α′. In addition, fine particles of the G-phase (structure type D8a, space group Fm\(\bar 3\)m) enriched in Si, Ni, and Mn have been found in intimate contact with the Cu precipitates. Following spinodal decomposition of the martensite phase, G-phase precipitation occurs after long-term aging.

Isothermal age-hardening behaviour in a multi-purpose dental casting gold alloy.

The isothermal age-hardening behaviour of a multi-purpose dental casting gold alloy was investigated by means of hardness testing, X-ray diffraction study, scanning electron microscopic observations and energy dispersive spectroscopy. By ageing of the solution-treated specimen at 400-500 degrees C, two phases of the Au-rich alpha 1 phase with an f.c.c. structure and the alpha 2 phase with an ordered f.c.c. structure based on Pt3In were transformed into three phases of the alpha 1 phase, the alpha 2 phase and the beta phase with an ordered f.c.t. structure based on PtZn. Hardening was attributed to the fine nodular precipitation resulting from the formation of the beta phase in the alpha 1 matrix. Softening was due to the coarsening of the fine nodular precipitates as the result of consumption of the alpha 2 phase.

Evolution and thermal stability of Ni3V and Ni2V phases in a Ni-29 at. pct V alloy

Eutectoid decomposition of the disordered fcc Ni-V solid solution in the composition range of 25 to 33.3 at. pct V gives rise to a mixture of the ordered Ni3V and Ni2V phases. In the present work, the evolution and thermal stability of these phases were studied in a Ni-29 at. pct V alloy. Solution-treated and water-quenched specimens, when aged at 850 °C, were found to exhibit two types of microstructure. In the first, the Ni2V phase precipitated in a lamellar Ni3V matrix where a pair of conjugate lamellae corresponded to two variants of the Ni3V phase. In the second morphology, the Ni2V phase precipitated within a Ni3V matrix comprising a single variant of the Ni3V phase. The Ni2V phase was observed to precipitate in a plate-shaped morphology, exhibiting {120}fcc-type, habit planes. The precipitation of the Ni2V plates in the Ni3V lamellae resulted in zigzag interfaces between adjacent Ni3V domains. Both the microstructures were found to be thermally quite stable and did not coarsen appreciably on prolonged aging. However, the prolonged aging caused the renucleation of the Ni3V and the Ni2V phases in the vicinity of the grain boundaries in a manner similar to “recrystallization.” The stability of the aged microstructure could be attributed to the nature of the interfaces between different domains of the Ni3V and Ni2V phases.

Injection moulding of inconel 718 aerospace components: J.Spirko et al. (Concurrent Technology Corp, USA.)

Inconel 718 was subjected to various heat treatments, i.e., solution heat treatment, standard ageing treatment and standard ageing plus 700 °C thermal exposure. The mechanical properties of the alloys were determined using tensile tests and Charpy pendulum impact tests at 650 °C and room temperature, respectively. The highest yield strength of 988 MPa was attained in the standard aged specimen, whereas a maximum impact toughness of 217 J cm−2 was attained in the solution-treated specimen. After thermal exposure, the mechanical properties of the specimens degrade. Both the yield strength and impact toughness decreased monotonically with increasing thermal exposure time. Subjected to a 10000-h long-term thermal exposure, the yield strength dramatically decreased to 475 MPa (almost 50% of the maximum strength), and the impact toughness reduced to only 18 J cm−2. The microstructures of the specimens were characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Coarsening of γ′ and γ″ and the transformation of γ″ to δ-Ni3Nb was observed after thermal exposure. However, a complete transformation from metastable γ″ to δ-Ni3Nb was never accomplished, even after the 10000-h long-term thermal exposure. Based on the obtained experimental results, the effects of the microstructural evolution on the mechanical properties are discussed.

Fatigue, Cyclic Deformation and Microstructure. Low Cycle Fatigue of Cu-Fe Alloy Single Crystals Containing Transformable Fe Precipitates.

Low-cycle fatigue behavior of Cu-1.53mass%Fe alloy single crystals with and without precipitated γ-Fe particles was examined. Although the γ-Fe particles are coherent and shearable, no cyclic softening was observed. Dislocation structures in solution-treated specimens were similar to those of fatigued pure Cu single crystals. However, in aged specimens, the precipitated γ-Fe particles retard the development of a dislocation structure. As a result, more uniform dislocation distribution compared with that in solution-treated specimens was observed, at least in the initial stages of cyclic deformation. Magnetic measurements revealed that the majority of the γ-Fe particles had transformed martensitically into x-Fe during the fatigue tests. The transformation changes the particle character from shearable to nonshearable. This change enhances the uniform deformation and the homogeneous dislocation distribution and leads to the absence of cyclic softening.

Experimental evidence for spinodal decomposition along with simultaneous ordering in Al-12.7 at% Li alloy

This paper deals with the phase transformation occurring during the early stages of ageing in Al-12.7 at% Li alloy. It is found that there is a sideband alongside the (200) main peak in the X-ray diffraction pattern of the solution-treated specimens. This implies that the phase separation in Al-Li alloys can occur by the spinodal decomposition mechanism, and that congruent ordering of solute atoms and precipitation of the δ′ (Al 3Li) phase take place simultaneously.

Temperature Dependence of the Tensile Behavior of Cast and Extruded Al–7Si–0.3Mg Alloys in 213–673 K

The temperature dependence of tensile properties of an A356 cast alloy is studied. The solution-treated, natural aged and peak aged specimens of the A356 cast alloy have been tensile tested in the temperature range of 213-673 K at the strain rate of 5.7 x 10 -4 s -1 . The data are also compared with that of extruded A356 specimens, in which more uniform silicon particles distribution is achieved. Independent of the particle distribution, both the cast alloy and the extruded alloy show a similar temperature dependence of tensile properties, implying that the tensile properties of the cast alloy are mainly determined by the precipitation of Mg 2 Si. At temperatures below about 573 K, the yield stress of the solution-treated cast specimens increases, while that of the peak aged specimens decreases gradually with increasing temperature. The yield stress of the natural aged specimens is nearly temperature independent. Corresponding to the high yield stress regime, the elongation of the solution-treated and natural aged specimens decreases drastically. At higher temperature at which dissolution of Mg 2 Si occurs, softening and recovery of the ductility are observed in all the specimens. On the temperature regime of about 223-373 K, the solution-treated specimens exhibit the Portevin-LeChatelier effect which is dependent on the concentration of vacancies and solute atoms. Since both vacancies and solute atoms are depleted during aging, the flow instability is absent in all aged specimens.

Fe-30%Cr合金の延性に及ぼす炭化物および窒化物の形態の影響

Effects of morphology of carbide and nitride precipitates on the ductility of Fe-30 mass%Cr alloys containing C from 0.002 to 0.044 mass% and N from 0.004 to 0.13 mass% were investigated. Three kinds of processes including heat treatments and cold rolling were adopted to obtain different types of morphology of carbide and nitride precipitates. Tensile tests were carried out at temperatures ranging from 4.2 K to room temperature. Ductility was evaluated by transition temperatures in reduction of area.The results obtained are summarized as follows:(1) Aging after solution-treatment gives rise to grain boundary precipitation of raft-like carbide or continuous plate-like nitride, while annealing without solution-treatment produces coarse globular carbide particle (5 μm) or fine spheroidal nitride particle (≤0.5 μm) within the grains. Aging after cold rolling of solution-treated specimen produced fine spheroidal carbide particle (≤0.5 μm) within the grains.(2) Even a small amount of plate-like grain boundary nitride brings about a drastic increase in transition temperature. Initiation of microcracks for brittle fracture may be caused by decohesion at the interfaces between the matrix and grain boundary precipitates, due to their continuous flat plate-like morphology. On the other hand, the effect of raft-like grain boundary carbide is less remarkable than grain boundary nitride.(3) Fine spheroidal nitride and carbide particles within the grains do not exert any detrimental effect on transition temperature, while coarse globular carbide leads to moderate increase in transition temperature.(4) In order to obtain improved ductility, it is recommended to choose a process condition in which precipitates are dispersed as fine particles within the grains.

Portevin-LeChatelier Effect of Al-7 mass%Si-Mg Cast Alloys

Al-7 mass%Si-Mg cast alloys can exhibit the Portevin-LeChatelier (PL) effect if excessive aging is prevented. In the present study, the PL effect of three Al-7Si-Mg cast alloys with 0.11, 0.26 and 0.46 mass% magnesium was compared with that of an Al-7 mass%Si cast alloy. Before conducting the tension test, part of the test alloys were solution treated at 813 K and the remaining were aged at 273 K. The critical strain for the onset of flow instability could be raised by increasing the magnesium content. For the solution-treated specimens tested in the low temperature regime where the critical strain decreases with temperature, the above result should be related to the attractive interaction between silicon and magnesium solutes since the apparent activation energy for the onset of flow instability increases with increasing magnesium content. For the solution-treated specimens tested in the high temperature regime, there occurs an aging effect which is more pronounced with increasing magnesium content and temperature. Consequently, the rate of increase of the critical strain for the ternary test alloys with respect to temperature is larger with higher magnesium content. For those specimens pre-aged at 273 K, the longer the aging time, the larger the critical strain. Also, the limiting aging time for which the flow instability still exists decreases with increasing magnesium content. Aging should play the role in depleting the quenched-in vacancies and solute atoms.