Effects of vanadium and cadmium on transformation temperatures of Cu–Al–Mn shape memory alloy

Cu-based quaternary shape memory alloys were extensively investigated alloy in last decade. In this study, Cu–Al–Mn, Cu–Al–Mn–V and Cu–Al–Mn–Cd shape memory alloys were produced by arc melting. We have investigated the effects of the alloying elements on the characteristic transformation temperatures, variations in structure and microstructure. The characterization of the transformation temperatures was studied by the differential scanning calorimetry. It was observed that the addition of the vanadium and cadmium decreases the characteristic transformation temperatures. The structural changes of the samples were studied by X-ray diffraction measurements and optical microscope observations. The crystal structure of the martensite Cu–Al–Mn, Cu–Al–Mn–V and Cu–Al–Mn–Cd shape memory alloys were identified as M18 at room temperature. The crystallite sizes of the alloys were determined. The microstructure of the alloy was studied with the help of optical microscope and V-type martensites with different orientations were detected. Microhardness value of the alloys were found between 194 and 211 Hv.     

Effects of high-energy-pulse-electron beam radiation on biomacromolecules

To study the molecular mechanism of high mutation frequency induced by high-energy-pulse-electron (HEPE) beam radiation, the effects of HEPE radiation on yeast cells, plasma membrane, plasmid DNA, and protein activity were investigated by means of cell counting, gel electrophoresis, AO/EB double fluorescent staining, etc. The results showed that the viability of yeast cells declined statistically with increase of absorbed doses. The half lethal dose (LD50) was 134 Gy. HEPE beam radiation had little influence on the function of plasma membrane and protein, while it could induce much DNA damage of single strand breaks (SSB) and double strand breaks (DSB) that were required for gene mutation. The G-value for DSB formation of HEPE beam radiation in aqueous solution was 5.7 times higher than that caused by 60Co gamma rays. HEPE can be a new effective method for induced mutation breeding and deserves further research in the future.     

Diffusion pack cementation of hafnium powder with halide activator on Ni–Ti shape memory alloy

The effect of a Hf chloride activator on the pack cementation of Hf powder on a Ni–Ti shape memory alloy wire was investigated. For this purpose, a Ni–Ti wire with a diameter of 0.5 mm was pack cemented in a powder mixture consisting of Hf and HfCl₄ powders at 1000 °C for 24 h. It was observed that Hf noticeably diffused into the Ni–Ti matrix with the aid of the HfCl₄ activator. The diffusion distance significantly increased as the amount of HfCl₄ activator increased. By the addition of 10 mass% HfCl₄, the martensite-to-austenite phase transformation start and finish temperatures increased from 12 to 142 °C and from 28 to 200 °C, respectively. The diffusion kinetics model was established based on Fick’s first law. It is suggested that 48 h of halide-activated pack cementation with 10 wt% HfCl₄ is necessary to increase the overall Hf content above 15 at.% throughout the Ni–Ti wire.     

The heating–cooling rate effect on thermal properties of high nickel-rich NiTi shape memory alloy

Journal of Thermal Analysis and Calorimetry - In this study, the effects of heating and cooling rate on the thermal properties of high nickel-rich Ni55Ti45 shape memory alloy were investigated....     

Influence of Ti additions on the martensitic phase transformation and mechanical properties of Cu–Al–Ni shape memory alloys

The effect of Ti additions on the microstructure and mechanical properties of Cu–Al–Ni shape memory alloys (SMA) was studied by means of a differential scanning calorimeter, field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction (XRD), a tensile test, a hardness test, and a shape memory effect test. The experimental results show that the Ti additions have an effective influence on the phase transformation behavior through generating a new phase into the microstructure, which is known as X-phase and/or controlling the grain size. The results of the XRD confirmed that the X-phase is a combination of two compounds, AlNi₂Ti and Ti₃·3Al. Nevertheless, it was found that with 0.7 mass% of Ti, the best phase transformation temperatures and mechanical properties were obtained. These improvements were due to the highest existence of the X-phase into the alloy along with a noticeable decrement of grain size. The Ti additions to the Cu–Al–Ni SMA were found to increase the ductility from 1.65 to 3.2 %, corresponding with increasing the strain recovery by the shape memory effect from 50 to 100 %; in other words, a complete recovery occurred after Ti additions.     

Liquid-phase synthesis and application of monolithic porous materials based on organic–inorganic hybrid methylsiloxanes, crosslinked polymers and carbons

Our recent progress in porous materials based on organic–inorganic hybrids, organic crosslinked polymers, and carbons is summarized. Flexible aerogels and aerogel-like xerogels with the polymethylsilsesquioxane (PMSQ) composition are obtained using methyltrimethoxysilane (MTMS) as the sole precursor. Preparation process and the flexible mechanical properties of these aerogels/xerogels are overviewed. As the derivative materials, hierarchically macro- and mesoporous PMSQ monoliths and marshmallow-like soft and bendable porous monoliths prepared from dimethyldimethoxysilane /MTMS co-precursors have been obtained. Organic crosslinked polymer monoliths with well-defined macropores are also tailored using gelling systems of vinyl monomers under controlled/living radical polymerization. The obtained polymer monoliths are carbonized and activated into activated carbon monoliths with well-defined pore properties. The activated carbon monoliths exhibit good electrochemical properties as the monolithic electrode. Some possibilities of applications for these porous materials are also discussed.     

Study of martensite transformation and microstructural evolution of Cu–Al–Ni–Fe shape memory alloys

In this study, variations in the transformation temperature, crystal structure, and microstructure of the arc melted alloy having nominal composition of Cu–13%Al–4%Ni–4%Fe (in mass%) were investigated for two different treatment conditions, homogenized and heat treated at 950 °C for 1 h. For both conditions, transformation temperature of the alloy was examined by DSC and it was determined as ~200 °C, similar to the value for Cu–Al–Ni alloys given in the literature. The crystal structure of the martensite Cu–13%Al–4%Ni–4%Fe (in mass%) alloy was identified as 18R using XRD. By heat treatment performed at 950 °C, diffraction peaks become more distinct. The microstructure of the alloy was studied with the help of optical microscope as a result of which parallel martensite plates and precipitates were detected. Microhardness value of the alloy was found as 361 and 375 Hv for homogenized and heat-treated conditions, respectively.     

The effect of e/a ratio on thermodynamic parameters and surface morphology of Cu–Al–Fe–X shape memory alloys

Journal of Thermal Analysis and Calorimetry - In this study, four Cu–Al–Fe–X shape memory alloys were produced by the arc melting technique, and the martensitic transformation...     

DSC analysis of Cu–Zn–Sn shape memory alloy fabricated via electrodeposition route

Cu–Zn–Sn shape memory alloy strips with composition range of 13.70–46.30 mass% Sn were fabricated by electrodepositing Sn on a shim brass surface and then subsequently annealed at a constant temperature of 400 °C for 120 min under flowing nitrogen. Subjecting the Sn-plated strips to differential scanning calorimetry (DSC) analysis revealed that the austenitic start (A _s) temperature was essentially constant at 225 °C while the martensite start (M _s) temperature was consistently within the 221.5–222 °C interval. Austenite to martensite phase transformation showed two distinct peaks on the DSC thermogram which can be attributed to the non-homogeneity of the bulk Cu–Zn–Sn ternary alloy. The latent heats of cooling and heating were found to increase with the mass% Sn plated on the shim brass. Effect of annealing temperature was also investigated wherein strips with an essentially constant composition of 26 mass% Sn were annealed at a temperature range of 350–420 °C for 120 min under flowing nitrogen. Varying the annealing temperature has no significant effect on the transformation temperatures of the ternary alloy.     

Rheokinetic cure characterization of epoxy–anhydride polymer system with shape memory characteristics

An epoxy resin capable of exhibiting shape memory property was derived by curing diglycidyl ether of bisphenol A (DGEBA) with a blend of carboxy telechelic poly(tetramethyleneoxide) (PTAC) and pyromellitic dianhydride (PMDA). The cure kinetics of DGEBA/PTAC/PMDA blend of varying compositions was investigated using isothermal rheological analysis. The overall reaction conformed to a second-order autocatalytic model. The kinetic parameters including reaction order, kinetic constants and activation energy were determined. The results showed that increase of PTAC decreased the overall activation energy and frequency factor of the cure reaction. This effect resulted in a diminution of the overall rate of curing. The catalysis by PTAC has its origin from the activation of epoxy groups by the protons of the COOH groups. The autocatalysis was caused by the COOH groups generated by the reaction of alcohol groups with anhydride. The activation energy for the autocatalysis was more than that for the primary reaction as the COOH groups responsible for autocatalysis were generated on a sterically hindered polymer backbone. The kinetics helped generate a master equation conforming to second-order autocatalytic model that could predict the cure profile of a specified resin system at a given temperature, leading to cure optimization.     

Effect of ball-milling conditions on microstructure during production of Fe–20Mn–6Si–9Cr shape memory alloy powders by mechanical alloying

Phase transitions associated with Fe?C20?wt% Mn?C6?wt% Si?C9?wt% Cr alloy during mechanical alloying and after subsequent annealing of that are studied experimentally. The conventional powder metallurgy route was used in preparing the sample. The milling time ranged from 5 to 20?h. Changes in microstructure as a function of milling time were investigated by using X-ray diffraction analysis, differential scanning calorimeter, and scanning electron microscopy. The grain sizes of powder milled are determined. The critical temperatures associated with the transformations are found to change with increasing ball-milling time.     

Unexpected chain length dependence on a chiral memory effect of ‘meta-ethynylpyridine’ oligomers

The chain length dependence involving a chiral memory effect of 2,6-pyridylene ethynylene oligomers ‘meta-ethynylpyridines’ was investigated. The meta-ethynylpyridine oligomers associated with octyl β-d-glucopyranoside form a helical complex giving induced CD; the induced chirality could be memorized with the help of Cu(OTf)₂ as an additive. Contrary to our expectations, the study of the length dependence revealed that the 12-meric oligomer showed a more sustainable chiral memory effect than those observed in both of the shorter 6-meric and longer 18-meric oligomers.     

Effects of nonlinear thermal radiation and activation energy on modified second-grade nanofluid with Cattaneo–Christov expressions

Journal of Thermal Analysis and Calorimetry - The aim of the current contribution is to exploit the effects of nonlinear thermal radiation and activation energy on the flow of modified second-grade...     

Precipitation sequence during ageing in β1 phase of Cu–Al–Ni shape memory alloy

The shape memory alloys based on the ternary system Cu–Al–Ni are able to produce a memory effect at high temperatures. However, if the material undergoes an accidental overheating, a transformation process leads to progressive loss of its characteristics. In this study, the effect of ageing on the metastable β₁ (austenite) phase of a Cu–13.3 %Al–4 %Ni shape memory alloy was investigated. In addition, the effects of heating rate between 450 and 580 °C on the structural transformations of austenite after cooling to room temperature were studied. Observation by transmission electron microscopy of the structure that has undergone an isothermal ageing shows that the precipitation process depends on the maximum ageing temperature. Furthermore, calorimetric analysis shows that precipitates dissolution is possible when rapid heating between 450 and 580 °C. This behaviour is observed on the cooling diagram which shows a martensitic transformation.     

Effect of metal-free porphyrins on the thermal–oxidative breakdown of biocompatible polymers

The inhibitory effect of metal-free porphyrins on the thermal–oxidative breakdown of several biocompatible polymers is observed for the first time. Differential thermal analysis shows that the thermal stability of poly(ethylene oxide) and triblock copolymers of ethylene oxide and propylene oxide increases by 80–100 K, compared to the initial breakdown temperatures of these polymers in the presence of metal-free porphyrins (up to 3 wt %).     

Correction to: The effect of e/a ratio on thermodynamic parameters and surface morphology of Cu–Al–Fe–X shape memory alloys

Journal of Thermal Analysis and Calorimetry - In the original publication of the article, the second author’s family name was incorrectly published.     

Carbon nanotube–polyurethane shape memory nanocomposites with low trigger temperature

Ester-based polyurethane (PU) with low glass transition temperature was used to develop shape memory nanocomposites with low trigger temperature. Pristine carbon nanotubes (CNTs) and oxidized CNTs (ox-CNTs) were introduced by melt mixing to improve the mechanical and shape memory properties of the PU matrix. The dispersion of CNTs on the mechanical properties and shape memory behaviors of the nanocomposites were also investigated. The results show that better dispersion of ox-CNTs contributes to more stiffness effect below glass transition temperature (T_g) while lower storage modulus (E′) above T_g. The nanocomposites exhibit high shape fixity and recovery ratio above 98%. The ox-CNT/PU nanocomposite shows higher shape recovery ratio for the first cycle, faster recovery due to better dispersion of CNTs and have potential applications for controlling tags or proof marks in the area of frozen food. The trigger temperature can be tailored by controlling the T_g of the PU matrix or the content of the nanofillers.