J.H. Sui

Microstructure and Mechanical Properties of Carboxylated Carbon Nanotubes/Poly(L-lactic acid) Composite

Poly(L-lactic acid) (PLLA)/MWNTs composites were prepared by mixing solubilized PLLA with solutions of MWNTs treated by four kind of acids. Fourier transform infrared (FT-IR) spectra revealed that carboxyl groups were grafted to the surface of MWNTs. The water solubility showed that the MWNTs treated by HNO 3/H2O2 and HNO3/H2SO 4 could suspend in the air at room temperature for more than 100 days. Thermogravimetric analysis (TGA) showed that MWNTs treated by HNO3/H 2O2 and HNO3/H2SO4 obtained relatively high COOH content. Mechanical properties of composites showed that the Youngs modulus of the carboxylated MWNTs/PLLA composites increased compared to the pure PLLA. Scanning electron microscopy (SEM) images of fracture morphology confirmed that the dispersion of carboxylated MWNTs was more homogeneous than the pristine MWNTs in polymer matrix. MWNTs treated by HNO3/H 2O2 could get more COOH group and less damage.Poly(L-lactic acid) (PLLA)/MWNTs composites were prepared by mixing solubilized PLLA with solutions of MWNTs treated by four kind of acids. Fourier transform infrared (FT-IR) spectra revealed that carboxyl groups were grafted to the surface of MWNTs. The water solubility showed that the MWNTs treated by HNO 3/H2O2 and HNO3/H2SO 4 could suspend in the air at room temperature for more than 100 days. Thermogravimetric analysis (TGA) showed that MWNTs treated by HNO3/H 2O2 and HNO3/H2SO4 obtained relatively high COOH content. Mechanical properties of composites showed that the Youngs modulus of the carboxylated MWNTs/PLLA composites increased compared to the pure PLLA. Scanning electron microscopy (SEM) images of fracture morphology confirmed that the dispersion of carboxylated MWNTs was more homogeneous than the pristine MWNTs in polymer matrix. MWNTs treated by HNO3/H 2O2 could get more COOH group and less damage.

Preparation of multi-walled carbon nanotube-reinforced TiNi matrix composites from elemental powders by spark plasma sintering

Carbon nanotube (CNT)-reinforced TiNi matrix composites were synthesized by spark plasma sintering (SPS) employing elemental powders. The phase structure, morphology and transformation behaviors were studied. It was found that thermoelastic martensitic transformation behaviors could be observed from the samples sintered above 800 °C even with a short sintering time (5 min), and the transformation temperatures gradually increased with increasing sintering temperature because of more Ti-rich TiNi phase formation. Although decreasing the sintering temperature and time to 700 °C and 5 min could not protect defective MWCNTs from reacting with Ti, still-perfect MWCNTs remained in the specimens sintered at 900 °C. This method is expected to supply a basis for preparing CNT-reinforced TiNi composites.

Effect of γ precipitates on martensitic transformation and magnetic properties in aged Mn–Ni–Ga alloys

Multiple martensitic transformation peaks were observed from differential scanning calorimetry curves in aged Mn50Ni25Ga25 alloys in which transformation temperature varied with aging temperature. The magnetization and coercivity were enhanced as a result of aging above magnetic transition temperature. A maximum magnetization up to 54emu∕g and a magnetization difference between two phases of 28emu∕g was achieved in the alloy aged at 873K. However, coercivity as large as 1.2kOe was obtained in 573K aged alloy, with a high saturation field, which can be understood in terms of domain wall pinning.

Processing of multi-walled carbon nanotube-reinforced TiNi composites by hot pressed sintering

Carbon nanotube (CNT)-reinforced TiNi matrix composites were synthesized successfully by employing elemental powders. Two methods have been used to control the interfacial reaction between CNTs and Ti, which heightened the quality of CNTs (graphitized multi-walled carbon nanotubes (GMWCNTs)) and shortened the time of over-eutectic temperature sintering (two-stage hot pressed sintering). It was found that a major TiNi parent phase with different proportions of intermetallic compound phases had been obtained by varying the second stage sintering temperatures. The specimens with second stage sintering temperature at 1050°C exhibited predominant mechanical properties, and the GMWCNTs retained their original size.Carbon nanotube (CNT)-reinforced TiNi matrix composites were synthesized successfully by employing elemental powders. Two methods have been used to control the interfacial reaction between CNTs and Ti, which heightened the quality of CNTs (graphitized multi-walled carbon nanotubes (GMWCNTs)) and shortened the time of over-eutectic temperature sintering (two-stage hot pressed sintering). It was found that a major TiNi parent phase with different proportions of intermetallic compound phases had been obtained by varying the second stage sintering temperatures. The specimens with second stage sintering temperature at 1050°C exhibited predominant mechanical properties, and the GMWCNTs retained their original size.

Effect of aging on martensitic transformation and microhardness of Ni53Mn23·5Ga18·5Ti5 ferromagnetic shape memory alloy

Abstract The effects of aging on martensitic transformation and microhardness were investigated for Ni53Mn23·5Ga18·5Ti5 ferromagnetic shape memory alloy. The results show that precipitation has obvious effect on martensitic transformation temperature and the microhardness increases with increasing aging temperature up to 973 K, and then decreases gradually with the further increase in aging temperature.

Microstructural characterisation and properties of quaternary Ni50Mn29Ga20Gd1 ferromagnetic shape memory alloy

Abstract A Heusler Ni50Mn29Ga20Gd1 ferromagnetic shape memory alloy is obtained by substituting 1 at-%Gd for Ga in a ternary Ni50Mn29Ga21 alloy. The microstructure, phase transformation, magnetic and mechanical properties of Ni50Mn29Ga20Gd1 alloy are investigated. It is shown that the Ni50Mn29Ga20Gd1 alloy has the best overall mechanical properties among the Ni50Mn29Ga21-xGdx (x = 0, 0·1, 0·5, 1, 2, 5) alloys. Compression tests show that a compressive strength of 1124·42 MPa with a compressive strain up to 16·25% can be achieved in this alloy. The mechanism of the improved mechanical properties is also discussed. The results demonstrate that the grains are refined obviously by the addition of 1 at-% Gd. The microstructure of the Ni50Mn29Ga20Gd1 alloy consists of the matrix and the hexagonal Gd(Ni, Mn)4Ga phase distributing mainly along the grain boundaries. Martensitic structure changes from five-layered martensite with 0 at-%Gd to seven-layered modulated martensite with 1 at-%Gd. One-step thermoelastic martensitic transformation occurs in this quaternary alloy. The martensitic transformation temperatures of the Ni50Mn29Ga20Gd1 alloy increase and its Curie temperature keeps unchanged compared with that of ternary Ni50Mn29Ga21 alloy. Coupling of the magnetic and structural transitions is observed in the Ni50Mn29Ga20Gd1 alloy.

Effect of structure on the optical properties of Ni-Mn-Ga alloy: experimental and theoretical investigation

Ni-Mn-Ga alloys possess thermoelastic martensitic transformation and ferromagnetic transition. Despite the giant magnetic-field-induced strain and stress-induced martensitic transformation developed in Ni-Mn-Ga alloys, however, little information is obtained about optical properties of Ni-Mn-Ga alloys as candidate materials in digital information storage. In this study, the optical reflectivity of Ni-Mn-Ga alloys in martensite and austenite phases has been investigated. The results reveal that the maximum reflectivity difference between the martensite and austenite phases is about 24%, indicating the promising application in phase-transition information storage. The calculated DOS shows that the effect of martensitic transformation on optical properties is attributed to the change of Ni 3d partial DOS between the austenite and martensite phases.