Elevated Temperature Tests Research Articles

Accelerated Stability Testing of a Water-in-Oil Emulsion

Non-optimal or non-predictable stability properties of emulsions can be limiting for the applications of emulsions. Therefore, it is of general interest to predict stability behavior. In the present study, accelerated stability testing employing elevated temperatures with good accuracy predicted long-term stability of a w/o emulsion stabilized with polyglycerol polyricinoleate (PG PR) kept at 4°C. It is argued that elevated temperature testing may successfully be applied to w/o emulsions provided that the phase inversion temperature is not crossed during the accelerated study. Furthermore, some qualitative effects of temperature on chemical stability could be observed. It was found that triglycerol polyricinoleate-6 provided the highest physical stability of four qualities of PG PR. Release characteristics of two entrapped hydrophilic markers, glucose and polyethylene glycol (m.w.4000) showed different sensitivities towards thermal stressing. The high releasing compound, glucose, showed a significant reduction in release rate in contrast to polyethylene glycol.

Effect of thermal annealing on plasticizer migration in poly(vinyl chloride)/dioctyl phthalate system

Plasticizer migration studies dealing with poly(vinyl chloride) (PVC) sheets and liquid surrounding media revealed two parallel phenomena, migration of plasticizer and liquid penetration, that take place simultaneously. The present work was focused on correlating the structural differences of the PVC material with the aforementioned processes. The plasticizer and the liquid medium used were dioctyl phthalate and isopropanol, respectively. Emphasis was placed on any rearrangement of the polymer morphology occurring when elevated test temperatures were employed for a relatively long period of time (crystallization). The result was that the PVC structure seemed to become more compact, forcing the liquid medium that had already penetrated to come out. Furthermore, these experiments showed that plasticizer migration and liquid penetration were related to the polymer structure. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1780–1786, 2001

Interfacial debonding and transverse properties of a Tiβ21s/SCS-6 composite

The transverse tensile and fatigue properties of a Tiβ21s/SCS-6 composite have been tested in the as-received condition, and after ageing at a temperature of 520°C for 8 hours. Interfacial debonding during the transverse tension has been defined using a combination of techniques of acoustic emission measurements, surface replication, repeated loading and unloading schedules, elevated temperature tests, and a theoretical analysis based on Eshelby's equivalent inclusion method. An intrinsic interfacial strength is deduced from experimental measurements, and this conclusion is supported by theoretical analysis and the trend of transverse behaviour with test temperature. The transverse fatigue crack growth resistance is dominated by that of the matrix, while the interfacial properties have a marked effect on the lives of fatigue crack initiation and short crack growth when the applied stress is lower than a certain level. Finite element calculations have been used to rationalise such observations.

酸化物分散強化型耐熱超合金のパルス通電焼結接合継手の機械的特性

In order to evaluate the mechanical properties of ODS superalloy joints bonded by pulsed electric-current sintering (PECS) technique, the tensile test at elevated temperature and creep rupture test were conducted for MA956 (Fe-based ODS alloy) and MA754 (Ni-based ODS alloy) joints. The ODS superalloys were bonded at 1323-1373 K for 0.9-64.8 ks in vacuum. The tensile properties at elevated temperature of completely densificated joints were almost comparable to those of base metal. However, the creep rupture lives of joints could be improved by the further holding at bonding temperature after the fully densification. The creep rupture lives of joint bonded for 64.8 ks reached about 70% of longitudinal directional life of base metal. TEM observations revealed that Cr2O3 inclusions existed on the prior particle boundary (PPB), and percentages of Cr2O3 inclusions on PPB were decreased with increasing the bonding time. The strengthen particles of oxide(Y2O3) were uniformly dispersed in the whole area of bonded interlayer without coagulating and coarsening. These results suggested that the improvement in creep rupture strength with bonding time was mainly attributed to the amelioration of the bonding strength of PPB.

Corrosion and wear studies of uncoated and ultra-thin DLC coated magnetic tape-write heads and magnetic tapes

Problems with corrosion and wear in magnetic tape drives lead the industry to consider the use of ultra-thin diamond-like carbon (DLC) coatings for tape heads and metallic tapes. In this study, corrosion and wear tests are conducted on uncoated and coated tape-write heads and tapes. A multi-component flowing mixed gas test, known as the Battelle Class II test, and an elevated temperature & humidity test are used to accelerate corrosion. While past researchers have evaluated corrosion effects by measurement of changes in magnetic properties of tape, surface analysis is successfully used here to study corrosion products directly. Corrosion specimens are examined using optical microscopy, Auger electron spectroscopy, scanning electron microscopy, and atomic force microscopy. Functional drive tests are conducted to measure the effectiveness of DLC coatings, deposited by ion beam, via study of pole tip recession (PTR) in tape heads. Heads are shown to benefit in both corrosion resistance and in PTR resistance from the addition of DLC. In both cases, 20 nm thick coatings outperform 10 and 5 nm thick coatings. Coatings on ME tape show some limited benefit in corrosion resistance. ME tape specimens exposed in cartridges show much less evidence of corrosion than those exposed outside of cartridges. MP tape shows better corrosion resistance than uncoated and coated ME tapes.

Balanced static elimination in variable ion mobility environments

Electrical ionizers with point-to-point and point-to-plane electrode arrangements were evaluated for use in static elimination systems. Elevated-temperature tests to 433 K were done in air, while reduced-temperature tests to 213 K were done in the vapors from liquid nitrogen. Balanced static elimination was obtained throughout the temperature range by controlling the ratio of the potentials on the positive and negative emitters, and allowing large free-electron currents from the negative emitters in the nitrogen environment. The charge-decay times were continuous through the nitrogen-to-air transition and dependent upon temperature as exp(const./ kT).

Deformation and fracture of Al 2O 3/Al–Zn–Mg–Cu metal matrix composites at room and elevated temperatures

Al 2O 3/Al–Zn–Mg–Cu metal matrix composites containing 2.22∼3.08 wt.% Mg in the matrix alloys have been fabricated by squeeze casting. The aim of the present study is to investigate the deformation and fracture behavior of the composites at RT (room temperature) and elevated temperature. Optical microscopy, scanning electron microscopy and image analysis were used to examine and to analyze the details of the microstructure and the fracture surface. Tensile tests were utilized to evaluate the mechanical properties from 25 to 400°C. The yield stress (YS) values and UTS values for all the composites were larger than those of monolithic alloys. The UTS values for composites and monolithic alloys increased with increasing Mg content. Elevated temperature tests indicated a good strength retention for the composites; especially, UTS values of the composites showed an improvement of 18% exceeds that of the monolithic alloys from 200 to 300°C. Significant dynamic strain aging occurred for composites; however, recovery and softening remained the dominant process for monolithic alloys in the range 25–300°C.

Tribology of tungsten disulfide–nanocrystalline zinc oxide adaptive lubricant films from ambient to 500°C

Tungsten disulfide (WS 2)–zinc oxide (ZnO) composite is a candidate material that exhibits adaptive lubricant behavior. Adaptive lubricants undergo chemical changes with changing environment to provide lubrication in extreme environments. In the current study, the tribological characteristics of WS 2–nanocrystalline ZnO films have been investigated from ambient to 500°C. The composite films were powder burnished on inconel substrates. Using a ball-on-flat tribometer, friction tests were conducted on WS 2–ZnO nanocomposite films containing 50% by weight of the oxide. For comparison, measurements were made on pure WS 2 films burnished under identical conditions. The room temperature tests were performed in dry nitrogen, while the elevated temperature tests were run in air. Wear scars and transfer films on the counterface were analyzed by scanning electron microscopy, energy dispersive X-ray spectroscopy and Raman spectroscopy. Results showed that the nanocrystalline ZnO additive resulted in significant reduction in friction coefficient of WS 2 both at 300°C as well as at room temperature. Third-body analyses from 300°C tests revealed that tribooxidation is less prevalent in nanocomposite films. At 500°C, the friction coefficient of pure WS 2 films increased to 0.50 within the first 2000 cycles, whereas the nanocomposite films lasted the entire duration of 10,000 cycles with steady state friction coefficient of 0.22. Raman spectroscopy identified the formation of zinc tungstate (ZnWO 4) during the 500°C tribotests, confirming the adaptive lubricant concept in WS 2–ZnO nanocomposites.

Correlation of fatigue and creep slow crack growth in a medium density polyethylene pipe material

The relationship between slow crack propagation in creep and fatigue in a medium density polyethylene pipe material was studied by increasing the R-ratio (defined as the ratio of minimum to maximum stress in the fatigue loading cycle) from 0.1 to 1.0 (creep). The study included characterization of the effects of R-ratio and temperature (21 to 80°C) on the mechanism and kinetics of slow crack propagation. With increasing R-ratio and decreasing temperature, the fracture mode changed from stepwise crack propagation, i.e. crack growth by the sequential formation and breakdown of a craze zone, to a “quasi-continuous” mode of crack growth through the preexisting craze. Despite the change in fracture mode, the damage zone, as characterized by the length of the main craze, shear crazes, and crack tip opening displacement, followed the same dependence on loading parameters, and crack growth rate followed the same kinetics. Crack growth rate (da/dt) was related to the maximum stress intensity factor KI, max and R-ratio by a power law relationship (da/dt) = B′K4I, max(1 + R)−6. Alternatively, crack growth rate was expressed as (da/dt) = B′KI4(t)Tβ(∈) with a creep contribution B‹KI4(t)›T, calculated by averaging the known dependence of creep crack growth rate on stress intensity factor KI over the period T of the sinusoidal loading curve, and a fatigue acceleration factor β(∈) that depended on strain rate only. The correlation in crack growth kinetics allowed for extrapolation to creep fracture from short-term fatigue testing. The temperature dependence of crack growth rate was contained in the prefactors B and B′. A change in slope of the Arrhenius plot of B′ at 55°C indicated that at least two mechanisms contributed to crack propagation, each dominating in a different temperature region. This implied that a simple extrapolation to ambient temperature creep fracture from elevated temperature tests might not be reliable.

Enhanced low dose rate sensitivity (ELDRS) of linear circuits in a space environment

To investigate the ELDRS effect in a real space environment, an experiment was designed, launched, and placed in a highly elliptical orbit in November 1997. After its deployment, the electrical responses of several bipolar transistors and linear circuits have been and continue to be recorded once during every 12-hour orbit. System dosimeters are monitored to establish an average accumulated dose per orbit. With this information, the electrical parameter data are correlated with the dosimetry data to determine the total dose response of each device. This paper updates information on the ELDRS experiment through May 14, 1999. As of this date, the experiment has been in flight for a period of 18 months and has accumulated an approximate dose of 18 krd(Si). For comparison, devices, specifically linear circuits with the same date code, were irradiated using Co-60 sources, herein defined as ground-based tests. The ground-based tests are used to evaluate two hardness assurance tests, a room temperature irradiation at 10 mrd(Si)/s and an elevated temperature irradiation at 100/spl deg/C and 10 rd(Si)/s and to evaluate the ELDRS response. To that end, irradiations were performed at room temperature, approximately 22/spl deg/C, at fixed dose rates of 100, 1, and 0.01 rd(Si)/s and at elevated temperature, approximately 100/spl deg/C, at a fixed dose rate of 10 rd(Si)/s. Currently, irradiations are being performed at room temperature at a fixed dose rate of 0.001 rd(Si)/s. Comparing the ground-based data to the flight data clearly demonstrates that enhanced parametric degradation has occurred in the flight parts. The two hardness assurance screens predicted ELDRS but the design margin for the elevated temperature test may not be adequate.

Analysis of Degraded Gold-Plated Surfaces in Contact With Lead-TiN Solder During Elevated Temperature Testing of 208- PIN Microelectronic Packages

Abstract This report provides analysis data on black deposits observed on gold-plated test socket pads. The socket pads are an integral part of a burn-in test where the test simulates an accelerated aging process and is routinely performed on new products. The test consists of placing a device, as shown in Figure 1, with lead/tin plated copper leads in a test socket then placing that assembly into a “burn-in” oven set to a specific elevated temperature, 150° C in this case, for a specific time. Typically, a bias voltage is applied through the pads on the socket during the test. Historically, during extended burn-in tests of Quad Flat Pack (QFP) devices, problems arose when several devices unexpectedly exhibited open socket-to-device contacts. The “opens” problem repeated itself when new QFP devices were installed in the sockets. Upon visual inspection of the sockets, black deposits were observed in the contact regions, as shown in Figure 2.

Mechanisms governing cyclic deformation and failure during elevated temperature fatigue of aluminum alloy 7055

The cyclic stress response, deformation and damage characteristics of aluminum alloy 7055 was studied at ambient and elevated temperatures. Specimens of the alloy were cyclically deformed using tension-compression loading under total strain-amplitude control. The alloy showed evidence of softening to failure at the ambient and elevated test temperatures. The degree of cyclic softening increased with an increase in test temperature. The presence of deformable matrix strengthening precipitates and particles in the T7751 microstructure resulted in a local decrease in resistance to the motion of “mobile” dislocations, causing a progressive loss of strengthening contributions to hardening. At the elevated temperatures, the occurrence of localized oxidation and embrittlement at the grain boundaries are promoted by the applied cyclic stress and play an important role in accelerating crack initiation and exacerbating stable crack propagation. The damage response of the alloy is discussed in terms of competing influences of intrinsic microstructural effects, matrix deformation characteristics arising from a combination of mechanical and microstructural interactions, cyclic plastic strain amplitude and concomitant response stress, and test temperature.

Elevated temperature deformation and crack growth behavior in titanium alloy 6-2222

Elevated temperature tests were performed on titanium alloy 6-2222 (Ti 6-2222) sheet material to determine the creep deformation behavior and to evaluate the suitability of crack tip parameters for characterizing creep crack growth behavior in the temperature range of 350–450°C. At temperatures of 400°C and above, the material behaves essentially as a creep-ductile material in which the creep crack growth rate is characterized by the C t parameter. At 350°C, transition from creep-ductile to creep-brittle behavior was observed. A correlation which is independent of temperature for creep-ductile conditions in the range of 350–450°C between creep crack growth rate and C t is derived from these tests. The creep-brittle behavior observed at 350°C was in the transient range where no well-accepted crack tip parameter is available for characterizing the crack growth behavior. A methodology for predicting creep crack growth in Ti 6-2222 sheet structures at elevated temperature when creep-ductile behavior is observed is briefly discussed.

The mechanical response and anti-extrusion characteristics of fibre-filled elastomers

The mechanical response and anti-extrusion characteristics of filled elastomers are examined in this paper. Both room-temperature and elevated-temperature uniaxial unconstrained compression and extrusion tests were carried out on hydrogenated nitriles (HNBRs) filled with carbon black and aramid fibres. The results suggest that fibre-filled HNBRs have a better resistance to extrusion over a range of extrusion gaps and temperatures. The level of extrusion resistance and the failure modes are related to the hardness and modulus of the material. It is shown that the current practice of using the hardness measured by conventional durometers to rank and/or select elastomers for specific applications may not be appropriate for elastomers with low concentration of fibres, as materials with nominally the same hardness have different resistances to extrusion and different compression moduli.

The effect of neutron dose, irradiation and testing temperature on mechanical properties of copper alloys

The paper presents the results of comparative investigations of radiation embrittlement of UHS–PH copper alloys of Cu–Ni–Be, Cu–Cr–Ni–Si type and the base Cu–Cr–Zr alloy after irradiation to 0.2 dpa at temperatures of 150°C and 300°C. The investigations undertaken and the analysis of changes in the mechanical properties of high-strength alloys of Cu–Ni–Be and Cu–Cr–Ni–Si irradiated to 0.2 dpa at 150°C and 300°C allowed for the conclusion that at low irradiation and testing temperatures alloys are prone to low-temperature embrittlement, which shows up in these alloys in the same way as in ITER base alloy. At elevated irradiation and testing temperatures the high-strength Cu–Ni–Be and Cu–Cr–Ni–Si alloys embrittle, and what is more, demonstrate, when irradiated, a low level of fracture stress (about twice as low as the initial material).

Effects of control mode in a cross-ply Ti-MMC at ambient and high temperature in air and in vacuum

Fatigue crack growth rates from unbridged defects in a [0/90°] 2s Ti–6Al–4V/SCS-6 cross-ply laminate composite have been measured to assess the effects of the control conditions under a stress ratio of R=0.1 and at a frequency of 10 Hz, whilst varying the initial stress intensity factor range (Δ K ini.), the test temperature and the environment. Initial fatigue crack growth rates in air were found to increase with increasing test temperature. Δ K ini. transition values leading to fatigue crack arrest compared with eventual specimen catastrophic failure are, at ambient temperature, approximately equal to 14 MPa√m in load control but are approximately 40% higher in position control. In addition, at a temperature of 450°C in air, the limiting value ofΔ K ini. promoting crack arrest decreases to 8 MPa√m in load control. In contrast, the Δ K ini. transition in vacuum at a temperature of 450°C is identical to that at ambient temperature in air under load control. Under position control at the elevated test temperature, a period of constant nominal stress intensity factor range (Δ K nom.) occurs. The crack growth rate at a test temperature of 450°C, in vacuum, is approximately 4×10 −7 mm/cycle in the constant Δ K nom. region, and this is somewhat less than that observed in air at the same test temperature (5×10 −6 mm/cycle), while crack arrest at ambient temperature in air is observed. Finally, it is suggested that position control experiments are of some advantage for the studies of the underlying crack growth mechanisms.

High Performance CuMetallized GaAs HEMTs Processing and Reliability

AbstractAlGaAs/GaAs based high electron mobility transistors (HEMTs) with Cu/Ti metallized gates have been fabricated. Copper gates were used to achieve low gate resistance and to minimize the hydrogen induced device degradation. The DC measurement of the processed AlGaAs/GaAs HEMTs with Cu/Ti gates shows comparable performance to similar Au based GaAs HEMTs. The Cu-based HEMTs were also subjected to elevated temperature testing under 5% H2 –N2 forming gas up to 250°C and 8 hours and no degradation due to hydrogen effects was found.

The fatigue and fracture of turbine blade alloys in high-pressure hydrogen : DeLuca, D.P. and Cowles, B.A. JOM (1996) 48 (11), 61–64

The roles of microstructure and environment in influencing mechanisms of damage during high-temperature, low cycle fatigue were investigated in a lithium-containing aluminium alloy in the peak-aged condition, and tested over a range of plastic strains. Reduction in fatigue life and resistance were observed at an elevated test temperature. Localized oxidation and embrittlement at grain boundaries are promoted by the applied stress, and play an important role in accelerating crack initiation and subsequent crack propagation. Evidence is presented to rule out contributions from microstructural changes through the coarsening of precipitate particles and the formation of new precipitate phases, and damage due to creep. The apparent acceleration of crack initiation and enhanced crack propagation are ascribed to a complex interaction of four mechanisms: intrinsic microstructural features, the embrittling effect of the environment, the slip mode arising from a combination of mechanical and microstructural contributions, and applied stress. The abnormal plastic strain-fatigue life by behaviour is attributed to differences in the distribution of deformation as a function of plastic strain amplitude.

Torsion test of aluminum in the large strain range

Abstract A series of experiments was conducted on cast and extruded high purity aluminum material under monotonic large strain torsion condition. Both free-end and fixed-end torsions were studied using tubular specimens of different gage lengths (long, medium and short). The experiments used an axial–torsional extensometer. A procedure of calibration for elevated temperature test was determined. The torque versus angle of twist curves were recorded and converted into true shear stress–strain curves by use of the modified Nadai method developed previously by the authors. The axial extension for free-end torsion and the axial stress developed during fixed-end torsion were recorded. The hoop strain was also measured and was found to be approximately 0.8–0.9 times the axial strain when the shear strain is 150%. The effect of specimen geometry was studied. It was found that the long, thick-walled tubular specimen is suitable for torsion test in the large strain range.

Hard particle erosion of silicon carbide and silicon carbide-titanium diboride from room temperature to 1000 °C

Two commercially available ceramics, a silicon carbide monolith and a silicon carbide-16 vol.% titanium diboride particle toughened ceramic matrix composite have been subjected to erosion by gas-borne silicon carbide particles over a range of experimental conditions, including erodent particle size and temperature. Material responses to single particle impacts and erosion have been correlated with the behaviour observed when the materials were subjected to quasi-static indentation by a sharp indenter. In all cases, material was lost through the mechanism of lateral fracture. The monolithic ceramic exhibited trends in behaviour which were consistent with the general predictions of wear models based on lateral cracking. The amount of material loss increased with the size of the erodent particles and with the test temperature. The composite material exhinited anomalous behaviour in some regimes. Generally, the composite had a lower wear rate than the monolithic material, as would be expected from its superior frracture toughness. When subject to erosion by the smallest of the three erodent sizes used, however, it exhibited a higher wear rate than the monolith and the wear rate was found to increase with decreasing particle size. This behaviour is not consistent with existing wear models but was consistent with observations of the quasi-static indentation testing. It is clear that the titanium diboride particles have an adverse effect on the short crack properties of the material. The elevated temperature testing employed a single particle size. The composite wear rate was always less than the wear rate of the monolith but the data converged as the temperature was increased, consistant with the decreasing ability of the titanium diboride particle to toughen the silicon carbide matrix.