Martensitic Transformation and Magnetic-Field-Induced Strain in Ni-Mn-Ga-RE （RE = Tb, Sm） Alloys

The effects of microamount additions of RE (Tb, Sm) on martensitic transition, the magnetic-field-induced strain and the bending strength of highly textured polycrystal line Ni4sMn33Ga19 alloy were investigated. The experimental results show that the addition of RE elements decreases the martensitic transformation temperature and the Curie temperature. But the bending strength of Ni-Mn-Ga-RE (RE=Tb, Sm) alloys increases remarkably because of the grain refinement. As a result, Ni-Mn-Ga-RE alloys will be applied practically with higher reliability and stability due to favorable plasticity and toughness. In addition, the replacement of small amounts Ga by Tb or Sm decreases the magnetic-field-in-duced strain of the alloys at room temperature.     

Electrospark powders of shape memory alloys

Powders of Ti-Ni and Ni-Mn-Ga alloys are obtained by the electrospark method. It is established that the largest particles are of irregular shape and the smaller ones are spherical. Some spherical particles are hollow. No carbon contamination is found within the Ti-Ni and Ni-Mn-Ga powders obtained in cryogen liquids. The Ti-Ni powders of all compositions are mixtures of austenite and martensite phases. Preliminary heat treatment of spherical-particle Ni-Mn-Ga alloys is needed to activate their martensitic transformation. The martensitic transformation proceeds over quite a wide temperature range, which is indicative of high dispersion, and the martensitic temperatures increase, which is indicative of a minor difference between the chemical compositions of powders and massive samples. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 5–6 (455), pp. 3–15, 2007.     

磁场对镍基Ni-Mn-Ga铁磁合金相变温度影响的热力学分析

通过测量磁化曲线、电阻-温度关系和热分析等手段,研究了磁场对镍基铁磁合金试样Ni-Mn-Ga相变的影响.结果表明：在磁场作用下相变温度升高了约1.5 K,具有明显的磁场影响特征.利用马氏体相变热力学理论,研究了磁场对镍基铁磁合金化学自由能和非化学自由能与温度的变化关系,建立了其作用的数理模型,并与实验结果比较后基本吻合.     

Phase Transformation Behaviors and Effects of Terbium in Polycrystalline Ni-Mn-Ga Magnetic Shape Memory Alloys

The phase transformation behaviors of two kinds of magnetic shape memory alloys NisoMn25 x Ga25-x and Ni50 Mn29Ga21-x Tbx were studied. When the composition of Ni in these alloys was constant, increasing Mn and reducing Ga contents make martensitic transformation temperatures rise obviously. Simultaneously, thermal hysteresis of phase transformation reduce but Curie temperature una|ters. When terbium was added, phase transformation temperature went up further and Curie temperature kept constant. The alloys still show strong ferromagnetism and properties of thermoelastic martensite phase transformation.     

Ni-Ti形状记忆合金中的相变

根据作者的工作、并结合新近文献,对近等原子Ni-Ti合金中的相变作了系统的综述,包括:相变的顺序,无公度相变,R相变,马氏体相变,合金成分及热循环对相变临界温度的影响,逆相变及沉淀。     

Ni-Ga-Fe-Co铁磁形状记忆合金的磁性转变和马氏体相变

Ferromagnetic shape memory alloys (FSMAs) such as NiMnGa, FePd and FePt are attractive as a new magnetic actuator material. They show a large magnetic-field-induced strain of 3% - 9% due to the variant rearrangement. Recently, the present authors have reported that in the Ni-Ga-Fe alloy the martensitic transformationfrom the B2 and/or the L21 structures into a seven-layer or five-layer modulated structure occurs upon cooling. In this alloy system, however, it is impossible to obtain a martensite phase at RT with a Curie temperature (To) higher than 100℃. In this work, the effects of substitution of Co for Ni on the martensitic and magnetic transformations, crystal structures and phase equilibria in Ni-Ca-Fe alloys were studied. Ni-Ga-Fe-Co alloys were prepared by induction melting under an argon atmosphere. Small pieces of specimens were taken from the ingot and homogenized at 1433 K for 24 h followed by quenching in water. The obtained specimens were aged at 773 K for 24 h and then quenched. The compositions of each phase were determined by energy dispersion X-ray spectroscopy (El)X). The martensitic transformation temperatures and Tc were measured by differential scanning calorimetry (DSC) and vibrating sample magnetometer (VSM) measurement. The crystal structure of martensite phase was observed by X-ray diffractmeter (XRD) and transmission electron microscope (TEM). The Curie temperature Tc was increased with increasing Co content while the martensitic transformation temperature slightly decreased. In the Ni(54-x) Ga27 Fe19 Cox, Tc increases from 303 K to 408 K with increasing CO content from x=0 to x=6. The crystal structure of the martensite phase and the phase equiribria in the Ni-Fe-Ga-Co alloys will be also presented.     

碳含量对Fe-15Mn-4.5Si-10Cr-5Ni-C系形状记忆合金性能的影响机制

 为通过调控碳含量获得形状记忆性能优异的铁基形状记忆合金,研究了3种不同碳含量对固溶时效态Fe-15Mn-4.5Si-10Cr-5Ni-C系形状记忆合金微观组织、力学性能及形状记忆效应的影响。结果表明,固溶时效态Fe-15Mn-4.5Si-10Cr-5Ni-(0.05~0.2)C合金的形状记忆效应随碳含量的增加呈现先增后减的趋势。这是由于一方面,随着碳含量的增加,碳原子的间隙固溶强化和第二相碳化物的沉淀析出强化提高奥氏体母相强度,抑制不可逆塑性变形的发生,有利于材料在受力时发生应力诱发奥氏体γ转变为ε马氏体(γ→ε),从而提高形状记忆效应。另一方面,全固溶温度随碳含量的增加而升高。由于全固溶温度的升高,固溶处理后得到的相对粗大的奥氏体晶粒造成奥氏体母相强度的降低。同时,随着碳含量的增加导致ε马氏体相变温度(M_εs)的降低,应力诱发相变过程受到抑制,不利于形状记忆效应。在不同影响机制的相互作用下,碳质量分数为0.091 8%固溶时效态试验合金的形状记忆性能最优。     

Co-Al二元系中的fcc/hcp马氏体相变和形状记忆效应

It is known that pure Co undergoes martensitic transformation from γ phase (fcc) to ε phase (hcp) by the movement of a/6<112> Shockley partial dislocations at around 400 ℃, however, there have been few systematic works on the SM effect in Co and Co-based alloys. In this study, the fcc/hcp martensitic transformation and the SM effect were investigated in Co-Al binary alloys(mole fraction of Al=0～16%).The γ/ε martensitic transformation temperatures were found from the DSC measurements to decrease with increasing Al content, while the transformation temperature hystereses were observed to increase from 60 ℃ at x(Al)=0 to 150 ℃at x(Al)= 16%. The SM effect evaluated by a conventional bending test was enhanced by the addition of Al over 4%(mole fraction) and Co-Al alloys containing over 10%(mole fraction) exhibit a good SM effect associated with the hcp →fcc reverse transformation above 200 ℃. The SM effect was significantly improved by precipitation ofβ (B2) phase and the maximal shape recovery strain of 2. 2% was obtained, which can be explained by precipitation hardening. The crystallographic orientations between theβ, ε and γ phases were also determined. Finally, the magnetic properties were investigated and it was found that the Curie temperature and saturation magnetization of Co-14% Al(mole fraction) are 690 ℃and 120 emu/g, respectively. It is concluded that the Co-Al alloys hold promise as new high-temperature and ferromagnetic SM alloys.     

Influence of Zn Addition on Microstructures and Martensitic Transformation in CuZr-based Alloys

Compositional dependences on microstructures and martensitic transformation behaviors in(Cu_(0.5)Zr_(0.5))_(100-x)Zn_x(x=1.5,2.5,4.5,7.0,10.0,and 14.0at.%)alloys were investigated.It was found that CuZr martensites were present in the present alloys.With increasing Zn content,the volume fractions of CuZr martensitic crystals and B2 CuZr phase gradually decrease and increase,respectively.With the addition of high Zn contents(i.e.,7.0,10.0,and 14.0at.%),the matrix proves to be eutectic.Thermal analysis results show that the initial martensitic transformation temperature(M_s)decreases from(412±5)K to(329±5)K as the Zn content increases from 1.5at.% to14.0at.%.The values of Msof Cu-Zr-Zn shape memory alloys are inversely proportional to the number and concentrations of valence electrons(i.e.,e_v/a and c_v),respectively,implying that the martensitic transformation in CuZrZn alloys could be of electronic nature.     

Dy对多晶Ni52Mn24.7Ga23.3合金马氏体相变和磁感生应变的影响

研究添加不同量的Dy对多晶Ni52Mn24.7Ga23.3的马氏体相变和磁性能的影响,发现合金的马氏体相变温度显著提高,并且随着Dy的增加,在一定的外应力的作用下合金的磁感生应变值增大,材料的抗弯性能也有着明显的提高。     

Tb对多晶Ni_(52.5)Mn_(23.5)Ga_(24)合金马氏体相变和磁感生应变的影响

研究了添加不同量的Tb对多晶Ni52.5Mn23.5Ga24的马氏体相变和磁性能的影响,发现合金的马氏体相变温度显著提高,而在不加外应力的作用下合金的磁感生应变值却有所下降。     

Ni_(43)Mn_(46-x)T_xSn_(11)(T=Fe,Co,Ni)合金的马氏体相变和磁熵变

通过示差扫描量热仪和振动样品磁强计对Ni43Mn46-xTxSn11(T=Fe,Co,Ni)铁磁形状记忆合金的相变、磁性以及磁熵变进行了研究。结果表明,由于价电子浓度的增加,Fe,Co,Ni替代Mn使马氏体转变温度大幅提高。Fe,Ni掺杂对马氏体居里温度(TCM)影响不大,Co则使TCM略有下降;奥氏体居里温度(TCA)对成分比较敏感,Fe,Ni的加入均使TCA略有提高,而Co则会大大提高TCA。由于马氏体相变伴随着磁化强度的突变,Ni43Mn46-xTxSn11合金在马氏体相变附近具有较大的低场磁熵变,对于Ni43Mn41Co5Sn11在室温1T磁场下磁熵变达到了19J.kg-.1K-1。通过调节成分,磁熵变峰值温度可以在199和294K之间调节,同时保持了较大低场磁熵变。     

Isothermal and athermal type martensitic transformations in yttria doped zirconia

The phase transformation from the high temperature tetragonal phase to the low temperature monoclinic phase of zirconia had been long considered to be a typical athermal martensitic transformation until it was recently identified to be a fast isothermal transformation. The isothermal nature becomes more apparent when a stabilizing oxide, such as yttria, is doped, by which the transformation temperature is reduced and accordingly the transformation rate becomes low.Thus it becomes easy to experimentally establish a C-curve nature in a TTT (Time-Temperature-Transformation) diagram. The C-curve approaches that of well known isothermal transformation of Y-TZP (Yttria Doped Tetragonal Zirconia Polycrystals), which typically contains 3mol% of Y2O3. In principle, an isothermal transformation can be suppressed by a rapid cooling so that the cooling curve avoids intersecting the C-curve in TTT diagram. Y-TZP is the case, where the stability of the metastable tetragonal phase is relatively high and thus the tetragonal phase persists even at the liquid nitrogen temperature. On the other hand, the high temperature tetragonal phase of pure zirconia can never be quenched-in at room temperature by a rapid cooling; instead it always turns into monoclinic phase at room temperature. This suggests the occurrence of an athermal transformation after escaping the isothermal transformation, provided the cooling rate was fast enough to suppress the isothermal transformation. Thus, with an intermediate yttria composition, it would be possible to obtain the tetragonal phase which is not only metastable at room temperature but athermally transforms into the monoclinic phase by subzero cooling. The objective of the present work is to show that, with a certain range of yttria content, the tetragonal phase can be quenched in at room temperature and undergoes isothermal transformation and athermal transformation depending on being heated at a moderate temperature or under-cooied below room temperature. Because both of the product phases are essentially the same monoclinic phase, both transformations are regarded as martensitic transformation, i. e. isothermal and athermal martensite. In some steels such as Fe-Mn-Ni and Fe-Ni-C, the occurrence of both isothermal and alhermal martensitic transformations has been reported. However, in these cases, the isothermal transformation occurs at temperatures slightly above the Ms (Martensite start) temperatures, and thus these transformations are considered to conform the same C-curve. On the other hand, the Ms temperature of the present material is well below the C-curve, which suggests that completely different mechanisms are controlling the kinetics of these two modes of transformations. Other aspects on these transformations are also to be reported..     

添加Y2O3的ZrO2的等温和变温马氏体相变

The phase transformation from the high temperature tetragonal phase to the low temperature monoclinic phase of zirconia had been long considered to be a typical athermal martensitic transformation until it was recently identified to be a fast isothermal transformation. The isothermal nature becomes more apparent when a stabilizing oxide, such as yttria, is doped, by which the transformation temperature is reduced and accordingly the transformation rate becomes low.Thus it becomes easy to experimentally establish a C-curve nature in a TTT (Time-Temperature-Transformation) diagram. The C-curve approaches that of well known isothermal transformation of Y-TZP (Yttria Doped Tetragonal Zirconia Polycrystals), which typically contains 3mol% of Y2O3.In principle, an isothermal transformation can be suppressed by a rapid cooling so that the cooling curve avoids intersecting the C-curve in TTT diagram. Y-TZP is the case, where the stability of the metastable tetragonal phase is relatively high and thus the tetragonal phase persists even at the liquid nitrogen temperature. On the other hand, the high temperature tetragonal phase of pure zirconia can never be quenched-in at room temperature by a rapid cooling; instead it always turns into monoclinic phase at room temperature. This suggests the occurrence of an athermal transformation after escaping the isothermal transformation, provided the cooling rate was fast enough to suppress the isothermal transformation. Thus, with an intermediate yttria composition, it would be possible to obtain the tetragonal phase which is not only metastable at room temperature but athermally transforms into the monoclinic phase by subzero cooling.The objective of the present work is to show that, with a certain range of yttria content, the tetragonal phase can be quenched in at room temperature and undergoes isothermal transformation and athermal transformation depending on being heated at a moderate temperature or under-cooled below room temperature. Because both of the product phases are essentially the same monoclinic phase, both transformations are regarded as martensitic transformation, i. e. isothermal and athermal martensite. In some steels such as Fe-Mn-Ni and Fe-Ni-C, the occurrence of both isothermal and athermal martensitic transformations has been reported. However, in these cases, the isothermal transformation occurs at temperatures slightly above the Ms (Martensite start) temperatures, and thus these transformations are considered to conform the same C-curve. On the other hand, the Ms temperature of the present material is well below the C-curve, which suggests that completely different mechanisms are controlling the kinetics of these two modes of transformations. Other aspects on these transformations are also to be reported..     

钐对Ni-B/SiO_2非晶态合金催化剂的催化性能及表面性质的影响

本文采用脉冲技术以己二腈气固相常压加氢为探针反应，研究了化学还原法制备的非晶态合金催化剂Ｎｉ－Ｂ、Ｎｉ－Ｂ－Ｓｍ的加氢活性及抗硫性能。并用Ｘ射线衍射（ＸＲＤ）、差示扫描量热分析（ＤＳＣ）、电感耦合等离子发射光谱（ＩＣＰ）、Ｘ射线光电子能谱（ＸＰＳ）、程序升温还原（ＴＰＲ）和程序升温脱附（ＴＰＤ）等手段对催化剂的结构、组成与表面性质进行了表征。实验结果表明，在此催化剂上该反应符合Ｌａｎｇｍｕｉｒ－Ｈｉｎｓｈｗｏｏｄ机理，活性中心座数为２。钐的加入可提高Ｎｉ－Ｂ非晶态合晶的热稳定性、催化活性和抗硫性。其原因可能是钐的给电子效应使合金的组成及表面性质发生了变化。     

Ni48Mn33Ga18Tb1合金的马氏体相变和磁性形状记忆效应

本文研究了 Ni48Mn3 3 Ga1 9合金添加微量的稀土元素 Tb后 ,对合金的马氏体相变、磁致应变性能及抗弯性能的影响 ,发现合金的马氏体相变温度、磁致应变值有所下降 ,而机械抗弯强度有显著提高。     

磁性形状记忆合金的研究现状及发展

磁性形状记忆合金是一种新发展起来的形状记忆材料，合金具有大恢复应变、大输出应力、高响应频率和可精确控制的综合特性，有望成为压电陶瓷和磁致伸缩材料之后的新一代驱动与传感材料。系统阐述了近年来磁性形状记忆合金的研究进展，并着重介绍了目前研究最多的Ni-Mn-Ga合金的结构、相变、形状记忆效应、制备方法及其在应用方面的一些新的研究成果，并提出了磁性形状记忆合金需要深入研究的问题及其发展方向。     

25MnVC钢的过冷奥氏体连续冷却转变曲线

采用Formastor-F全自动相变仪测定了25MnVC钢的连续冷却转变曲线(CCT曲线),研究了其在不同冷却速度下的组织转变规律。通过与25MnVK钢的CCT曲线相比,发现由于奥氏体化温度的差异和添加了Cr元素的原因,25MnVC钢的先共析转变和珠光体转变一直持续发生直至马氏体转变前,扩大了贝氏体相变区域,并提高了Ms点温度,减小了马氏体转变临界冷却速率。     

Ni53Mn22Ga25磁性形状记忆合金的相变内耗

研究了Ni53Mn22Ga25磁性记忆合金在190～390K温度范围的内耗行为。结果表明．当合金发生正、逆马氏体相变时出现明显的内耗峰,并伴随模量变化出现极小值。马氏体相变后继续降温。在215K附近出现新的内耗峰,模量明显增高。合金在居里温度发生顺磁及铁磁正反转变时．内耗及模量均不发生变化。对上述现象进行了分析和讨论。     

Influence of cooling rate on magneto-structural transition and magnetocaloric effect of Ni30Cu8Co12Mn37Ga13 alloy

The influence of heat treatment with different cooling rates on phase transition behaviors and magnetocaloric effect is systematically studied.Difference in atomic order is induced by changing cooling rates,where ordered phase is obtained in the furnace cooled(FC)sample while disordered phase is reserved in the water quenched(WQ)sample.The coupled magneto-structural transition is detected in both samples but the characteristic temperature significantly shifts to lower temperatures with increasing atomic order.Giant magnetic entropy change(ΔS_(mag))derived from magnetic field induced martensitic transformation is confirmed for both samples,and can be remarkably enhanced by the atomic ordering.The largestΔS_(mag) of 20.9J/(kg·K)is obtained at 307.5Kunder 5Tin the FC sample.