Magnetocaloric effect of Pr2Fe17−x Mn x alloys

Polycrystalline Pr2Fe17-xMnx（x = 0, 1, and 2）alloys were studied by X-ray diffraction（XRD）, heat capacity, ac susceptibility, and isothermal magnetization measurements. All the alloys adopt the rhombohedral Th2Zn17-type structure. The Curie temperature increases from 283 K at x = 0 to 294 K at x = 1, and then decreases to 285 K at x = 2. The magnetic phase transition at the Curie temperature is a typical second-order paramagnetic–ferromagnetic transition. For an applied field change from0 to 5 T, the maximum-△SM for Pr2Fe17-xMnxalloys with x = 0, 1, and 2 are 5.66, 5.07, and 4.31 J·kg^-1·K^-1,respectively. The refrigerant capacity（RC） values range from 458 to 364 J·kg^-1, which is about 70 %–89 % that of Gd. The large, near room temperature △SM and RC values,chemical stability, and a high performance-to-cost ratio make Pr2Fe17-xMnxalloys be selectable materials for room temperature magnetic refrigeration applications.     

Effect of Si on the reversibility of stress-induced martensite in Fe–Mn–Si shape memory alloys

Fe–Mn–Si is a well-characterized ternary shape memory alloy. Research on this alloy has consistently shown that the addition of 5–6 wt.% Si is desirable to enhance the reversibility of stress-induced martensite vis-à-vis shape memory. This paper examines the effect of Si on the morphology and the crystallography of the martensite in the Fe–Mn–Si system. It is concluded that the addition of Si increases the c/a ratio of the martensite, reduces the transformation volume change and decreases the atomic spacing difference between the parallel close-packed directions in the austenite–martensite interface (habit) plane. It is proposed that, in addition to austenite strengthening, Si enhances reversibility by reducing the volume change and the interfacial atomic mismatch between the martensite and the austenite. Although shape memory is improved, transformation reversibility remains limited by the necessary misfit dislocations that accommodate the atomic spacing differences in the interface.     

Intermetallic phase formation in directionally solidified Al−Si−Fe alloy

The present study has been undertaken to better understand the solidification behavior of Al−Si−Fe alloys containing 7wt.% Si and 0.9wt.% Fe, with particular regard to the formation of phase during controlled solidification and influence of growth rates on intermetallic phase selection. The alloys studied were Al-7Si-0.9Fe alloys, which were produced by a modified Bridgman solidification arrangement. These alloys were solidified unidirectionally with different growth rates (1–30mm/min). The solidified microstructure of these alloys consists of the growth of primary aluminum and multiple second phase reactions.     

Mn—Fe熔体的脱Si过程及Mn—Fe熔体氧位研究

通过实验（１３５０℃ ）测定 Ｍｎ－ＭｎＯ２平衡体系 Ｍｎ液氧位,验证了 ＺｒＯ２（ＭｇＯ）固体电解质定氧探头可用于测定 Ｍｎ－Ｆｅ熔体和锰液氧位．电动势－氧位换算关系式为 ｌｎ ｐｏ２－３１．５６－（６９５４８．８＋４６４２７．７×Ｅ）／Ｔ．使用 ＢａＣＯ３７０％－ＭｎＯ２５％－（Ｆｅ２Ｏ３＋ＢａＦ２）２５％（质量分数）的熔剂对高炉 Ｍｎ－Ｆｅ脱 Ｓｉ时,与最高脱 Ｓｉ率（７５％）对应的 Ｆｅ２Ｏ３含量是１２％; Ｍｎ－Ｆｅ熔体中氧位和 Ｃ的活度关系式为 ｐｏ２× １０１２＝３５．８１２－０．１０６×ａｃ; Ｍｎ－Ｆｅ熔体中氧位和 Ｍｎ损（　［Ｍｎ］）关系为ｐｏ２×１０１２＝６．２３８＋０．６７９×　［Ｍｎ］．使用 ＢａＣＯ３６０％－ＢａＦ２１０％－ＭｎＯ２１５％－Ｆｅ２Ｏ３１５％熔剂对高炉 Ｍｎ－Ｆｅ脱Ｓｉ时, 最高脱 Ｓｉ率（８８．９％）和最高氧位（８．３１×１０－１２ Ｐａ）对应的脱 Ｓｉ时间为 １５ ｍｉｎ．脱 Ｓｉ实验结果表明：脱 Ｓｉ过程中Ｍｎ－Ｆｅ熔体的氧位是由熔体中碳氧反应控制的;脱 Ｓｉ保 Ｍｎ的最高氧位是 ６．２３８×１０－１２ Ｐａ．     

Fe—Mn—Si合金的磁转变

利用电阻测量、Ｘ射线衍射等方法研究了铁锰基形状记忆合金中γ→ε相变与顺磁－反铁磁转变。对顺磁－反铁磁转变的温度区间和可逆性作了仔细分析。降温时→ε转为与顺磁到反铁磁转变的温度区间有重叠，但升温时反铁磁到顺磁的转变出现在－１４０℃到＋５０℃之间，ε→γ在１００－２００℃之间进行，二者截然分开     

Fe－Mn－Si合金的磁转变

利用电阻测量、Ｘ射线衍射等方法研究了铁锰基形状记忆合会中γ→ε相变与顺磁—反铁磁转变（ＰＭ－ＡＭ）．对顺磁—反铁磁转变的温度区间和可逆性作了仔细分析。降温时γ→ε转变与顺磁到反铁磁转变的温度区间有重叠，但升温时反铁磁到顺磁的转变出现在－１４０℃到＋５０℃之间，ε→γ在１００～２００℃之间进行，二者截然分开，淬火态合会Ｘ射线谱上的奥氏体线条强于马氏体线条，即奥氏体是主相。结果还表明磁转变表现为降温时电阻由下降转为升高。Ｎｅｅｌ转变点由升温曲线上的最低点给出，其值为－５℃。讨论了Ｓｉ对磁转变影响的可能原因。     

Effect of cooling rate and Fe/Mn weight ratio on volume fractions of α-AlFeSi and β-AlFeSi phases in Al−7.3Si−3.5Cu alloy

The crystallization behavior of iron intermetallic compounds in Al?7.3Si?3.5Cu alloy was investigated using thermal analysis, metallography, and a thermodynamic simulation performed with the Scheil module of ThermoCalc^®. We observed that β-AlFeSi disappeared when both high (>3.5°C/s) and low cooling rates (<0.1°C/s) were used. The elimination of β-AlFeSi at low cooling rates may be attributable to a decrease in the magnitude of microsegregation associated with low cooling rates. The disappearance of β-AlFeSi at high cooling rates may be related to growth difficulties when this phase precipitates during solidification of eutectic Al?Si: β-AlFeSi precipitation approaches the solidification onset of eutectic Al?Si when the cooling rate is increased. Moreover, the cooling rate at which the β-AlFeSi phase is suppressed should depend on the chemical composition of the alloy. According to thermodynamic simulations, the alloy composition determines the precipitation onset temperature of both β-AlFeSi (T _β) and eutectic Al?Si (T _eut). The cooling rate at which the β-AlFeSi phase disappears may be even higher as the difference betweenT _β andT _eut increases.     

Phase analysis of the mechanically alloyed Fe−Si powder by differential dissolution technique

The binary Fe?Si elemental powders mixture (1∶2 in atomic proportion) has been milled for different milling times in an attrition mill. The phase characterization of mechanically alloyed powder was investigated using the chemical method of differential dissolution (DD) and the X-ray diffraction (XRD) method. In powder specimens milled for more than 15 hr, ∈-FeSi and unreacted Si were observed. The formation of a supersaturated solid solution of Si in ∈-FeSi induced by mechanical alloying (MA) was also verified. The lattice parameter of the ∈-FeSi of as-milled powders changed from 4.4876 Å to 4.4668 Å according to the increase of MA time. Based on the results of the DD analysis, unreacted Si could be classified as (1) crystalline Si, (2) Si supersaturated in ∈-FeSi, or (3) amorphous Si. Therefore formation of the β-FeSi₂ after annealing could be explained by the reaction between the ∈-FeSi and the Si classified into types (1) and (2). It seemed that the amorphous Si induced by MA did not react with the ∈-FeSi during annealing at 700°C.     

Structure and properties of Fe−Cr−Mn steels after quenching with preheating in the intercritical temperature interval

Conclusions The quenching of high-alloy chromium-manganese steels, which includes preheating in the intercritical (+) temperature interval and subsequent short-term austenitizing, the latter eliminating homogenization of the -solid solution, increases the dispersity of the martensite and stabilizes the austenite.In this case, the strength and plastic properties of the steels are improved as compared with normal quenching.Mariupol' Metallurgical Institute. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 6, pp. 45–47, June, 1990.     

Kinetics of Oxidation of Fe–6Si

Surface oxidation of Fe–6Si during annealing in low-pressure air (～10⁴ Pa) in the temperature range 500–550 °C was investigated using resistivity measurements, Mössbauer spectroscopy, X-ray diffraction and scanning-electron microscopy (SEM). The time dependence of the resistivity exhibits an increase in two steps, which indicates changes in the structure and/or phase composition of the alloy. Structure and phase investigations show that the first step can be explained as formation of hematite (α-Fe₂O₃) and the second step is due to transformation of the hematite to magnetite (Fe₃O₄). The kinetics of the transformations were derived from the resistivity data. The activation energies (estimated from Arrhenius plots) of 194 kJ/mol and 165 kJ/mol were obtained for the formation of hematite and transformation of hematite to magnetite, respectively.     

Fe—30Mn—6Si形状记忆合金的M_s

Ｆｅ—３０Ｍｎ—６Ｓｉ形状记忆合金的Ｍ_ｓ为了获得可罪的形状比忆效应，必须精密控制形状Ｕ忆合金的马氏体转变温度（Ｍ）和奈耳温度（几）。什一＊ｎ一ｂ形状地忆合金由于价格低血且容易加上，故极受重视。含Ｍｎ兆％～３４％和Ｓ讨％～６．５。龙的Ｆｅ一Ｍｎ一出合?..     

The ductility and strength of Fe−Cr−Al alloys

Metal Science and Heat Treatment -     

Effect of Al addition on microstructure and mechanical properties of Mg−Zn−Sn−Mn alloy

The microstructure and properties of the as-cast, as-homogenized and as-extruded Mg−6Zn−4Sn−1Mn (ZTM641) alloy with various Al contents (0, 0.5, 1, 2, 3 and 4 wt.%) were investigated by OM, XRD, DSC, SEM, TEM and uniaxial tensile tests. The results show that when the Al content is not higher than 0.5%, the alloys are mainly composed of α-Mg, Mg₂Sn, Al₈Mn₅ and Mg₇Zn₃ phases_. When the Al content is higher than 0.5%, the alloys mainly consist of α-Mg, Mg₂Sn, MgZn, Mg₃₂(Al,Zn)₄₉, Al₂Mg₅Zn₂, Al₁₁Mn₄ and Al₈Mn₅ phases. A small amount of Al (≤1%) can increase the proportion of fine dynamic recrystallized (DRXed) grains during hot-extrusion process. The room- temperature tensile test results show that the ZTM641−1Al alloy has the best comprehensive mechanical properties, in which the ultimate tensile strength is 332 MPa, yield strength is 221 MPa and the elongation is 15%. Elevated- temperature tensile test results at 150 and 200 °C show that ZTM641−2Al alloy has the best comprehensive mechanical properties.