Vibration cavitation behaviour of selected Ni-Mn-Ga alloys

Vibration cavitation erosion tests were carried out on Ni-Mn-Ga alloys of three different crystal structures: (1) the cubic austenite, (2) the non-modulated tetragonal martensite (T) and (3) the five-layered martensite (5M). All Ni-Mn-Ga alloys exhibited cavitation behaviour characterized by a step-wise curve of mass loss versus test time. This behaviour is correlated to the microstructural nature of the alloys as well as the surface conditions of the pre-test samples. The type and concentration of the defects at the surfaces were critical to the cavitation resistance of the alloys. The best cavitation resistant alloy was of a cubic austenitic structure, followed with the alloy of a tetragonal T-martensite. The largest material loss was found in the alloy with a 5M martensite. All the studied Ni-Mn-Ga alloys had an excellent cavitation resistance compared to that of the reference stainless steel, and they even excelled some NiTi alloys found in literature. This may be due to the superelasticity of the cubic austenite and the twinning of the martensitic phases.     

Large magnetic-field-induced strains in rare earth polycrystalline Ni-Mn-Ga

The magnetic-field-induced strains (MFIS) of polycrystalline Ni50Mn29Ga21 alloys containing Tb were studied. A large MFIS of-1.10% was obtained under compressive prestress conditions. The addition of Tb can fine the crystal grains, enhance the bending strength obviously, and make MFIS increase further, indicating that a moderate amount of Tb does not hinder twin boundary motion and it conversely makes the material more practical.     

Formation of texture of Ni48Mn31Ga21 polycrystalline alloy by thermal simulation pack rolling technology

1 Introduction Heusler type Ni2MnGa magnetic shape memoryalloy, which is a new kind of functional material withferromagnetism and thermoelastic martensitictransformation, attracts the interests of many people allover the world in recent years. The alloy …     

Ni50Mn27Ga23快淬薄带的马氏体相变和磁感生应变

采用快淬技术制各了非化学计量成分的Ni50Mn27Ga23多晶薄带，对快淬薄带的马氏体相变和磁感生应变进行了研究。结果表明，快淬薄带侄冷却和加热过程中仍然发牛热弹性马氏体相变及逆相变，具有典型的热弹性形状记忆效应，并且比铸态合金具有更大的应变，但是马氏体相变温度下降。快淬工艺在合金内部引入特定的内应力，使薄带形成织构，是合金获得更大相变应变和磁感卞应变的原因。热处理后，内应力大大降低，导致磁感牛应变降低。     

预变形对Ni-Mn-Ga合金马氏体相变的影响

研究了形变对Ni-Mn-Ga合金马氏体相变及其组织形态的影响，并应用马氏体相变热力学和动力学探讨了适当塑性变形后马氏体相变滞后得以大幅度提高的微观本质。结果表明，随着应变量的增加，马氏体相变温度几乎保持不变，而其逆相变温度则迅速升高，塑性应变导致储存在界面处的弹性应变能的释放是塑性变形提高合金相变滞后的主导因素。     

铁磁形状记忆合金Ni-Mn-Ga薄膜制备工艺研究

铁磁形状记忆合金（FSMA）是种新型智能材料，Ni—Mn—Ga合金是这种材料的典型代表。本文使用ECR磁控溅射方法在NaCl晶片上制备出了Ni—Mn—Ga薄膜，并对其制备溅射功率进行了探讨。通过对薄膜成分和表面性质的分析，知22．5W为其制备的最佳功率。对沉积在玻璃片上的薄膜进行衍射分析各其为有序化程度不高的晶态。     

Effect of Rare Earths on Electronic Structure of (110) Twin Martensite Boundary for Ni2MnGa Alloy

The doping effect of rare earth elements (Tb and Sm) on the electronic structure of (110) martensitic twin boundary in Ni2MnGa alloys was investigated by using ab initio method within the DFT and the supercell implementation. The calculated results show that the atomic relaxation lowers the boundary energy and the segregation energy. Sm seems easier to segregate to the boundary and has a greater doping effect compared with Tb due to its lower segregation energy and bigger bonder order with neighboring atoms. Tb makes a greater contribution to the magnetic properties of the twin boundary than Sm.     

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。     

稀土多晶Ni-Mn-Ga铁磁记忆合金的马氏体孪晶与磁感生应变

铁磁性形状记忆合金Ni-Mn-Ga是一种新型功能材料,它在磁场作用下能产生大的应变.研究了Ni50Mn29Ga21Tb1.2室温下的晶体结构和磁感生应变,并用O'Handley的解析模型分析合金产生大磁感生应变的原因是马氏体孪晶在磁场下的迁动.     

新型磁驱动形状记忆合金研究进展

磁驱动形状记忆合金是一种新型功能材料,由于兼具大的输出应变和高响应频率等综合特性,成为智能材料领域的研究热点之一.本研究首先总结了Ni-Mn-Ga合金在相变和磁致应变性能方面的特点,然后着重介绍了Co-Ni-Ga和Ni-Fe-Ga两类新型磁驱动记忆合金在结构、相变、形状记忆效应、磁性能等方面的研究进展,并对其中存在的问题进行了讨论.