Hardness of surfacing alloys at elevated temperatures

Conclusions Of all the surfacing materials tested the greatest hardness at elevated temperatures is exhibited by electrodes made by the cermet method using chromium carbide as a base, i.e., GK-10 and GK-15 with a metal binder.Translated from Poroshkovaya Metallurgiya, No. 3 (51), pp. 80–83, March, 1967.     

Creep-rupture behavior of iridium at elevated temperatures

The creep-rupture properties of annealed arc-cast iridium were determined between 982°C and 1288°C for times less than 1000 h. It was found possible to fit the rupture and creep results by the Sherby-Dorn parameter method using an activation energy of 70,600 calJmole. It was found that under creep deformation, failure was at least partially intercrystalline, and the failure elongation decreased with increasing temperature and time.     

Plastic deformation of titanium at elevated temperatures

The deformation of iodide titanium single crystals containing 200 to 250 ppm O, was studied in compression at temperatures from 25° to 800°C. Reduction of about 5 pct along thec axis was accommodated almost entirely by \(\left\{ {11\bar 22} \right\}\) twinning from 25° to 300°C, and above 400°C by \(\left\{ {10\bar 11} \right\}\) twinning in combination with c+a slip. The stress for \(\left\{ {11\bar 22} \right\}\) twinning increased with increasing temperature, and twin formation was accompanied by a load drop, while the stress for \(\left\{ {10\bar 11} \right\}\) twinning decreased with increasing temperature and twinning was not accompanied by a load drop. Crystals reduced normal to thec axis deformed by a combination of prism slip and \(\left\{ {10\bar 12} \right\}\) twinning at 25°C and by prism slip alone above 500°C.     

Creep-rupture behavior of iridium at elevated temperatures

The creep-rupture properties of annealed arc-cast iridium were determined between 982°C and 1288°C for times less than 1000 h. It was found possible to fit the rupture and creep results by the Sherby-Dorn parameter method using an activation energy of 70,600 calJmole. It was found that under creep deformation, failure was at least partially intercrystalline, and the failure elongation decreased with increasing temperature and time.     

Proof strength values for austenitic stainless steels at elevated temperatures

The influence of the alloying elements C, N, Si, Mn, Cr, Ni, Mo, Cu, Ti on proof strength is studied in the temperature range 20–550 °C. High temperature data for the proof strength of austenitic stainless steels have been analysed. Using computational thermodynamics the amount of alloying elements in solid solution and the volume fractions of precipitates were assessed. These quantities were then applied in a regression analysis for the high temperature strength. Quantitative relationships for the proof strength as a result of the regression analysis are proposed as a function of temperature. They are to be used in materials design. The interstitial elements showed the largest effect. Si, Ni and Mo increased the strength at all temperatures. Cu and Mn reduced the strength and Cr gave an influence, which varied with temperature.     

Fatigue limit of ceramic materials at elevated temperatures

Translated from Poroshkovaya Metallurgiya, No. 2(350), pp. 42–47, February, 1992.     

Fatigue of Ni-Ai-Mo aligned eutectics at elevated temperatures

The elevated-temperature mechanical behavior of two aligned eutectics (Ni-8.1 wt pct Al-26.4 wt pct Mo and Ni-6.3 wt pct Al-31.2 wt pct Mo) has been investigated utilizing monotonic and cyclic testing in vacuum. Tensile yield strength and fatigue resistance increased from 25 to 725 °C, but then were reduced at 825 °C. The fatigue lives of specimens tested at 725 °C decreased sharply with decreasing frequency. A shift from surface to internal crack initiation was observed upon increasing the test temperature from 725 to 825 °C. Stage II crack propagation was observed at both temperatures, in contrast to stage I cracking at 25 °C. The test results are compared to those for other nickel and cobalt-base aligned eutectics to show that the frequency effect on fatigue life is not limited to the Ni-AI-Mo system. formerly Graduate Assistant in the Department of Materials Engineering, Rensselaer Polytechnic Institute     

Mechanical properties of ultra-high-strength steels at elevated temperatures

ABSTRACT

This paper presents an experimental study on the mechanical properties of ultra-high-strength steels at elevated temperatures. Tensile tests were carried out at 300–600°C on Docol 1200M and Docol 1400M steel samples. The results indicate that as the temperature increases Young’s Modulus, yield strength (YS) and ultimate tensile strength (UTS) display a decrease. YS/UTS ratios at 300°C are lower than those at room temperature, they make peaks at 400 and 500°C for Docol 1400M and Docol 1200M, respectively, and then decrease again beyond those temperatures. While total elongation continuously increases, uniform elongation slightly decreases with increasing temperature. Present carbides in tempered matrix continue to grow and new carbides are observed at the grain boundaries. Considering all roll forming parameters, 300°C seems the most convenient temperature for warm forming. In this sense, the warm roll forming has a potential for forming complex-shaped parts by reconciling strength with formability.     

Fast separations at elevated temperatures on polybutadiene-coated zirconia reversed-phase material

This paper describes the results of thermal stability studies of polybutadiene-coated zirconia reversed phases and application to fast HPLC separations at elevated temperatures and high flow rates. The thermal stability of the material was evaluated at temperatures up to 200 degrees C, and the rapid analyses of polyaromatic hydrocarbons and typical reversed-phase test mixtures were carried out at 100 degrees C and a flow rate of 5 mL/min. We found that the material is completely stable at 200 degrees C for at least 1300 column volumes. Analysis time can be decreased about 18-fold at high temperatures and flow rates without any significant loss in resolution relative to that at conventional temperatures and normal flow rates. For the separation of a five-component reversed-phase test mixture, the analysis time was only 50 s.     

Modelling on flow stress of plain carbon steel at elevated temperatures

A predictable model to estimate the true stress-true strain response of plain carbon steel has been made being divided into the two ranges of α- and γ-iron respectively. Again, for the (α + γ)-range, the mass fraction of the two phases has been taken into consideration. As a result, the peak stress as well as the stress-strain relation calculated by the model have been found to be in fairly good agreement with those measured by a few investigators under various temperature and strain rate conditions. In particular, concerning the peak stress, it has been confirmed that the model gives a remarkable good conformability, compared with the measured values. Also, the peak stress exhibits the discontinuous change at the A₃ point. However, with an increasing carbon content, the discontinuous point tends to shift toward the lower temperature side, and the changing degree becomes slighter.     

Oxidizability of materials based on TiC and TiN at elevated temperatures

Conclusions The addition of titanium nitride and niobium carbide to the alloys based on TiC with the nickel-molybdenum binder (TN type) increases their oxidation resistance in air at high temperatures (1173–1273°K). The alloys based on the titanium carbide and nitride and alloyed with the niobium carbide with the nickel-molybdenum binder (NTN) have higher oxidation resistance in air than the commercially produced TN20 and T15K6 alloys.The equations of the kinetic curves of oxidation in air of the TN20 and NTN alloys were derived; at temperatures of 1173 and 1273°K, the curves are almost linear, starting at a holding time of 10 min.Translated from Poroshkovaya Metallurgiya, No. 4(304), pp. 76–78, April, 1988.     

The deformation and fracture of TiAl at elevated temperatures

The tensile properties of the intermetallic compound TiAl have been determined at several temperatures in the range 25 to 1000°C. Additional variables studied were the influence of strain rate and the effect of exposure to oxidizing conditions prior to testing. The modes of deformation under the various testing conditions were studied in the electron microscope, the modes of fracture were studied in the scanning electron microscope, and these data were correlated with the mechanical properties. The results indicate that the ductilebrittle transition behavior of TiAl at about 700°C is controlled by the trailinga/6 [112] partial dislocation components of thea [011] superdislocations overcoming their pinning barriers. It was also shown that prior exposure to oxidizing conditions does not markedly influence the mechanical properties of TiAl.     

A mathematical model for flat rolling of austenitic steel at elevated temperatures

The paper is concerned with the mathematical model for the computation of the technological as well as force and energy parameters during rolling of austenitic steel sheets and strips at elevated temperatures. On the basis of the computation results obtained for 18–8 type chromium-nickel steel (marked 1H18N9T) universal nomograms have been designed for a wide range of strip width and roll diameters. They allow the evaluation of force parameters, energy consumption and average temperature in the roll pass depending on the reduction and strip initial temperature as well as strip relative thickness. The presented nomograms might be helpful in designing the technology for warm rolling of austenitic steel sheets and strips as well as conventional cold-rolling, taking into consideration thermal effects in the deformation zone.     

Detecting short periods of elevated workload: A comparison of nine workload assessment techniques.

The present experiment tested the merits of 9 common workload assessment techniques with relatively short periods of workload in a car-driving task. Twelve participants drove an instrumented car and performed a visually loading task and a mentally loading task for 10, 30, and 60 s. The results show that 10-s periods of visual and mental workload can be measured successfully with subjective ratings and secondary task performance. With respect to longer loading periods (30 and 60 s), steering frequency was found to be sensitive to visual workload, and skin conductance response (SCR) was sensitive to mental workload. The results lead to preliminary guidelines that will help applied researchers to determine which techniques are best suited for assessing visual and mental workload. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Morphological stability of copper-silver multilayer thin films at elevated temperatures

The kinetics of breakdown of Cu-Ag polycrystalline multilayers during aging at elevated temperatures was investigated. Microlaminates with Cu:Ag layer thicknesses of 2:2, 1:4, 4:1, and 4:0.1 μm were aged for 10 minutes to 192 hours (t), at temperatures ranging from 700 to 900 K. The asdeposited microlaminates had a fine-grained columnar microstructure with well-defined interfaces. Upon annealing, the morphology evolved over three time regimes. In the first regime, the grains in each phase grew quickly to an apparent terminal size, which depended on both the layer thickness and annealing temperature. Next, grooves formed at the intersections of grain boundaries and layer interfaces and grew with a t ^0.25 dependence. The groove growth appeared to be independent of layer thickness and was approximately equal in Cu and Ag. The microlaminates started to break down in the third regime, as grain-boundary grooves on opposite sides of a layer bridged its thickness. Models for grain growth and grooving in thin films were modified for multilayer microlaminates and were shown to fit the experimental data reasonably well. This suggests that the terminal grain size is reached when groove drag overcomes the capillary forces driving grain growth, and that grooving kinetics are dominated by interfacial diffusion.     

The erosion behavior of 304 stainless steel at elevated temperatures

The objective of this paper is to characterize the solid particle erosion behavior of an annealed 304 stainless steel (SS) over the temperature range of 300 to 763 K. Silicon carbide was used as the erodent. Impact velocity and angle were kept constant at 115 m/s and 90 deg (normal), respectively. The results indicated that the erosion rate of 304 SS as a function of test temperature went through a minimum at around 548 K. None of the empirical models or parameters proposed in the literature for correlating room-temperature erosion resistance with a variety of mechanical or thermophysical properties of the eroding or erodent material explained the observed erosion ratevs temperature behavior. However, the results were qualitatively explained on the basis of a localization model for erosion. An analysis of the erosion data also indicated that oxidation of the eroding material and related effects on erosion were unimportant even at the highest test temperature of 763 K.