Investigation of the heat conductivity of niobium in the temperature range 0.05–23 K

We report thermal conductivity measurements on a single-crystal niobium specimen of resistivity ratio 33,000 over the temperature range 0.05–23 K in the superconducting state and above 9.1 K in the normal state. The axis of the niobium rod was [110] oriented. The surface roughness was varied by sandblasting of the sample. The values of the thermal conductivity in the range from the lowest temperatures up to the maximal value covered a range of six orders of magnitude (=2×10^–5 W cm^–1 K^–1 at 50 mK to =22 W cm^–1 K^–1 at 9 K). Above 2 K the results for the untreated and the sandblasted sample are in accord, whereas below 2 K the influence of the sample surface is discernible. The various conduction and scattering mechanisms are discussed.     

The effect of DO3 ordering on the parent ⇄ martensitic transformation in the CuZnAl shape-memory alloy

The character of D03 ordering resulting from different quenching rates and its effect on the characteristic martensitic transformation temperatures and shape-memory effect in the Cu-21.5 at % Zn-12.5 at % Al alloy has been analysed. ln room temperature water-quenched samples with a cooling rate 1000° C sec^–1 showing B2 long-range order and DO₃ Short-range order, e significant stabilization of martensite in the reverse transformation was observed. This stabilization was eliminated in the air-cooled samples with a cooling rate 20° C sec^–1 showing DO₃ long-range order. Mechanical tests revealed a more complete shape recovery in the air-cooled samples, when compared to room temperature waterquenched ones.     

Experimental studies of the heat capacity of liquid octene-1 in the temperature range 282–368 K

Results are presented on the heat capacity c_p of octene-1 in the temperature range 282–368 K. The present experimental data are compared with results in the literature.Academic Scientific Complex A. V. Luikov Heat and Mass Transfer Institute, Academy of Sciences of Belarus, Minsk. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 66, No. 4, pp. 490–491, April, 1994.     

The effect of deformation on γ-ε martensitic transformation in an Fe-Mn-Mo alloy

Effect of prior plastic deformation of austenite on the martensite start temperature, volume fraction and strength of martensite have been studied in an Fe-14.3%Mn-3.7%Mo alloy. Mo was chosen to examine the possible effect of the third alloying element in an Fe-Mn based alloy and the obtained results were compared with those of the Fe-Mn binary alloys given in the literature. Predeformation of austenite created considerable changes on the formation characteristics and also the strength of the martensitic phase and the obtained results were discussed in terms of the dislocations formed during the deformation process.     

Indirect determination of martensitic transformation temperature of sintered nickel-free Ti–22Nb–6Zr alloy by low temperature compression test

Nickel-free Ti–22Nb–6Zr alloys were fabricated by conventional powder metallurgy sintering method. X-ray diffractometer (XRD) investigation showed that the as-sintered alloys mainly consisted of β phase, with a few needle-like α phase precipitates. Differential scanning calorimetry (DSC) measurement in the temperature ranging from −70 °C to 400 °C and constant stress thermal cycling test by dynamic mechanical analysis (DMA) were unable to reveal the martensitic start temperature of sintered Ti–22Nb–6Zr alloys. Therefore low temperature compression tests were carried out to evaluate their phase transformation behavior indirectly. There was an obvious drop of both Young’s modulus and recoverable strain at −85 °C ∼ −80 °C in the Young’s modulus-temperature and recoverable strain–temperature curves of sintered Ti–22Nb–6Zr alloys respectively, which was attributed to the occurrence of thermal elastic martensitic transformation at this temperature. At the testing temperature of −85 °C, a superelasticity of as high as 5.9% was achieved in the sintered alloys. The results had revealed that sintered Ti–22Nb–6Zr alloys own a great superelasticity intrinsically and would exhibit a much greater superelasticity at room temperature if their martensitic transformation start temperature (M_s) were closer to room temperature. Along with their noble biocompatibility, sintered nickel free Ti–22Nb–6Zr alloys are thus thought to be potentially competitive biomaterials for biomedical applications.     

The decomposition of the solid solution state in the temperature range 20 to 200° C in an Al-Zn-Mg alloy

The decomposition of the supersaturated solid solution of an Al-3.2wt% Zn-2.2 wt% Mg alloy has been investigated in the temperature of 20 to 200° C, by small-angle X-ray scattering, electrical resistivity and mechanical measurements. On the basis of the results obtained, three subsequent stages of the decomposition process can be distinguished. Between 20 and 70° the basic process is the nucleation and growth of G.P. zones, the volume fraction of which increases logarithmically with time. A transition stage is observed between 80 and 100° in which the volume fraction increases linearly with time. Above 90° C, the growth kinetics of the volume fraction shows a definite incubation period at the beginning of ageing, while the yield stress increases monotonically. In the temperature range 100 to 160° C, the formation of the phase takes place. Below 100° a linear connection between the yield stress and (fR)^1/2 is found from which the specific surface energy to cut a G.P. zone is calculated to be ₀= 0.21 Nm m^–2.     

Effect of thermal cycling on martensitic transformation temperatures in Ti–Ni–Cu shape memory alloys

Abstract

Changes in martensitic transformation temperatures during thermal cycling in Ti–Ni–Cu shape memory alloys have been investigated by means of electrical resistivity measurements, thermal cycling tests under constant load and transmission electron microscopy. During thermal cycling without applied stress, the B2→B19′ transformation temperature M _s decreased, while the B2→B19 transformation start temperature M _s′ kept almost constant. During thermal cycling with applied stress, in solution treated Ti–45Ni–5Cu alloy, changes in M _s depended on the amount of applied stress. That is, M _s decreased when the applied stress was 39.2 MPa, while its value kept almost constant when a stress of 117.2 MPa was applied. It was also found that M _s′ increased during thermal cycling in the solution treated Ti–35Ni–15Cu and Ti–30Ni–20Cu alloys, irrespective of the amount of applied stress. All changes in M _s and M _s′ during thermal cycling with applied stress in Ti–Ni–Cu alloys were explained well by a combination of the thermal cycling effect and the structural refinement effect.     

Kinetics of the ω phase transformation of Ti-7333 titanium alloy during continuous heating

Dilatometry method was used to study the ω phase transformation kinetics of a near-β titanium alloy Ti–7Mo–3Cr–3Nb–3Al during continuous heating. The local activation energy as a function of transformed volume fraction f _ω was determined by Kissinger–Akahira–Sunose (KAS) method, which increases with the transformation proceeding and the average value is about 85.06 kJ/mol. The nucleation and growth mechanism of the ω phase was investigated by the non-isothermal local Avrami exponent n, which appears a significant change with the transformed volume fraction, indicating that the transformation mechanism varies at different stages. The local Avrami exponent lies between 0.5 and 2 in a wide transformed volume fraction range of 0.05–0.9, indicating that the dominating mechanism of ω phase transformation in Ti-7333 titanium alloy is the three-dimensional growth with a near-zero nucleation rate.     

Influence of thermal cycling on the martensitic transformation and shape memory effect of a Fe－16Mn－

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Influence of strain rate on the temperature rise of specimens in static tests of a titanium alloy in the 293–4.2 K range

The influence of two strain rates, 1.10^–1 and 2.10^–2 sec^–1, on the temperature rise of specimens of -titanium alloys in static tests in the 290- 4.2 K range is investigated. It is established that at room temperature conditions (290 K) the temperature rise of the specimens is nonuniform over the length and is 14 K, in liquid nitrogen (77 K) it is more than 0.5 K, and in liquid helium (4.2 K) the temperature depends upon the strain rate and reaches 46 K. It is shown that the temperature rise of the specimens in liquid helium in strain at a rate of 2.10^–2 sec^–1 reduces the tensile strength but does not influence the yield strength of the material.Translated from Problemy Prochnosti, No. 12, pp. 70–78, December, 1992.     

Coherency strains influence on martensitic transformation of γ-Fe particles in compressed Cu-Fe alloy single crystals

Single crystals of a Cu-Fe alloy, which contained spherical -Fe particles, were compressed up to shear strain of 0.17 in liquid nitrogen bath. In the process of straining the structural (optical and TEM) observations in as-deformed and post-deformation annealed samples were provided. The substructure of deformed samples was characterized by slightly developed cell structure and lack of distinct layer-like arrangements of dislocations. Three kinds of particles were found: coherent and semi-coherent f.c.c. -Fe and martensiticly transformed b.c.c. -Fe. The critical diameter for coherency loss was found to be 58 nm at the initial stage of deformation decreasing with strain to 50 nm. These values coincided with the theoretical estimations. It was suggested that relaxation of coherency strains around -Fe particles by the generation of interface dislocations might occur prior to the martensitic transformation. This assumption might explain the particle size dependency of martensitic transformation.     

Generalization of experimental specific heat data for synthetic corundum in the temperature range 80–300°k

The results of an experimental investigation of the specific heat of corundum on state standard GÉT 70–75 are given. The possibility of generalizing the most accurate data to expanded batches of corundum is discussed.Notation c specific heat - T absolute temperature - c_calc calculated values of specific heat - c_exp experimental values - c=[(c_exp–C_calc)/c_exp]·100% relative deviations of experimental values of specific heat - f theoretical normal curve of relative errors Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 4, pp. 664–670, October, 1980.