Ni-Mn-Ga-Gd structure of high temperature memory alloy and shape memory effect

Title: Ni-Mn-Ga-Gd structure of high temperature memory alloy and shape memory effect Author: Zhang Xin Degree-granting unit: Harbin Institute of Technology Keywords: Ni-Mn-Ga alloy;; high temperature memory alloy;; mechanical properties;; shape memory effect;; rare earth Gd Summary:

In this paper, scanning electron microscopy, transmission electron microscopy analysis, X-ray diffraction analysis, differential scanning calorimetry, room Neodymium magnets temperature compression test methods such as systematic study Ni_ (54) Mn_ (25) Ga_ (21-x) Gdx (x = 0 , 0.1,0.2,0.5,1,2) the organizational structure of shape memory alloy and shape memory effect; clarify the Gd doping on the phase composition, martensitic transformation, mechanical properties and the influence of the shape memory effect and mechanism. The study found that rare-earth doping of Gd Ni-Mn-Ga alloy grain refinement, with the Gd content increases, the grain size decreases. Ni-Mn-Ga-Gd alloy microstructure of the matrix and second phase. With the increase of Gd content, the number of the second phase increase, larger size, and mainly distributed along the grain boundaries.

The results showed that, Ni-Mn-Ga-Gd alloys occurs during heating and cooling step thermoelastic martensitic transformation and reverse transformation. With the Gd content increases, the phase transition temperature first increases, then decreases and then increases. The main reason for this result is the matrix alloy composition of Ni and Mn content changes very little with Gd, while the Ga content is changed greatly by the impact of changes in Ga content to Ni-Mn-Ga-Gd alloys Markov changes in body temperature fluctuations. Gd content on the Ni-Mn-Ga alloy martensitic type does not have a significant impact, the alloy matrix has been non-modulated tetragonal martensite.

Compression test results show that the rare earth Gd doping can significantly improve the Ni-Mn-Ga alloy mechanical properties. Gd content in the alloy compression fracture strength and fracture strain has a significant influence. In the Gd content of 1at.%, The compression fracture strength and fracture strain reaches the maximum value. With the increase of Gd content, matrix hardness increased gradually, and the hardness of the second phase was significantly http://www.chinamagnets.biz/Neodymium/Ball-Neodymium-Magnets.php greater than the alloy matrix. Gd doping changes the Ni-Mn-Ga alloy fracture mode. Ni-Mn-Ga alloy fracture mode to intergranular fracture, very brittle; as Gd content increases, the alloy gradually transformed into transgranular cleavage fracture, fracture toughness occur more frequently torn edges, increased plasticity;

Studies have shown that the shape memory effect, Gd doping elements increase the Ni-Mn-Ga alloy shape memory effect, Gd content of 1at.% Maximum when the shape memory effect; Ni_ (54) Mn_ (25) Ga_ (20) Gd1 alloy in the pre-deformation of 3%, the response can be completely, reversible shape memory strain of 1.8%; when the alloy pre-deformation of 4%, the greatest of shape memory reversible strain is 1.9%, the shape Memory response rate was 87.5%. And Ni_ (54) Mn_ (25) Ga_ (21-x) Gdx alloys have two-way shape memory effect. Degree Year: 2010