Decreasing Test Temperature Research Articles

Rotary-bending fatigue characteristics of medical-grade Nitinol wire

The rotary bending fatigue properties of medical-grade Nitinol wires were investigated under conditions of 0.5–10% strain amplitudes to a maximum of 107 cycles. The results from this study provide insight into the behavior of Nitinol under fully reversed (εmin/εmax=−1) fatigue conditions for three compositions, two surface conditions and three test temperatures. For pseudoelastic conditions there are four distinct regions of the strain-cycle curves that are related to phases (austenite, stress-induced martensite, and R-Phase) and their respective strain accommodation mechanisms. In contrast, there are only two regions for the strain-cycle curves for thermal martensite. It was further observed that the strain amplitude to achieve 107-cycles increases with both decreasing test temperature and increasing transformation temperature. Fatigue behavior was not, however, strongly influenced by wire surface condition. SEM of the fracture surfaces showed that the fatigue fracture area increased with decreasing strain amplitude. Finite element analysis was used to illustrate strain distributions across the wire as well as to calculate the tension-compression contributions to the rotary bending curves. The results from this investigation are discussed with respect to mechanisms of strain accommodation under cyclic tensile and compressive conditions.

Stress-induced transformation behaviors at low temperatures in Ti-51.8Ni (at. %) shape memory alloy

Martensitic transformation behaviors at low temperatures in polycrystalline Ti-51.8Ni (at. %) alloy were investigated with compressive stress. Superelasticity with almost complete shape recovery was confirmed at temperatures of 40–180 K. In stress-induced transformation at fixed temperatures, while the reverse transformation finishing stress monotonically decreased with decreasing test temperature, the forward transformation starting stress changed from decrease to increase at about 125 K. Forward and reverse transformation temperatures evaluated under constant stresses of 50 and 750 MPa were generally coincident with the results determined at the constant temperatures, where “heating-induced forward transformation” was confirmed under a stress of 750 MPa.

Investigation of microstructure and mechanical properties of novel Sn–0.5Ag–0.7Cu solders containing small amount of Ni

This work investigates the effects of small additions (0.05 and 0.1wt.%) of Ni on the microstructure and mechanical properties of low Ag content Sn–0.5Ag–0.7Cu (SAC (0507)) lead-free solder alloy. The addition of 0.05Ni resulted in the microstructural refinement, uniform distribution of the Ag3Sn and (Cu,Ni)6Sn5 intermetallic compounds (IMCs) and small primary β-Sn grains. This apparently enhances the mechanical strength and microhardness. However, the addition of 0.1Ni leads to the formation of relatively high fraction of the primary β-Sn phase and the IMCs appeared abrasive within the matrix. As a result, the SAC (0507)–0.1Ni solder exhibits low tensile strength, microhardness and large elongation, which produce a soft and highly compliant bulk solder. In addition, the strength of all studied alloys increases with increasing strain rate and decreasing testing temperature, showing strong strain rate and temperature dependence. Based on the obtained stress exponents and activation energies, it is proposed that the dominant deformation mechanism in SAC (0507) solders is dislocation climb over the whole temperature range investigated.

Effect of Mn concentration on the kinetics of strain induced precipitation in Ti microalloyed steels

The kinetics of strain induced precipitation in Ti-microalloyed steel with three levels of Mn was investigated using a two-stage interrupted compression (TSIC) test. The precipitation-time–temperature diagrams (PTT) were obtained by analyzing the softening kinetics curves of deformed austenite. Experimental results showed that the upper part of the PTT diagram for strain induced precipitation were shifted to lower temperatures and longer times as Mn concentration in steel was increased, but the retard effect of Mn on TiC precipitation weakened with decreasing testing temperature. Transmission electron microscopy (TEM) observation showed that the rate of TiC precipitation was decreased by more Mn addition at higher testing temperatures, which is in a good agreement with TSIC result. In addition, these results were discussed in terms of the effect of Mn on the solubility product of TiC in austenite, and the controlling factors of precipitation kinetics at different temperatures.

On the Effects of Hot Forging and Hot Rolling on the Microstructural Development and Mechanical Response of a Biocompatible Ti Alloy

Zr, Nb, and Ta as alloying elements for Ti alloys are important for attaining superior corrosion resistance and biocompatibility in the long term. However, note that the addition of excess Nb and Ta to Ti alloys leads to higher manufacturing cost. To develop low-cost manufacturing processes, the effects of hot-forging and continuous-hot-rolling conditions on the microstructure, mechanical properties, hot forgeability, and fatigue strength of Ti-15Zr-4Nb-4Ta alloy were investigated. The temperature dependences with a temperature difference (ΔT) from β-transus temperature (Tβ) for the volume fraction of the α- and β-phases were almost the same for both Ti-15Zr-4Nb-4Ta and Ti-6Al-4V alloys. In the α-β-forged Ti-15Zr-4Nb-4Ta alloy, a fine granular α-phase structure containing a fine granular β-phase at grain boundaries of an equiaxed α-phase was observed. The Ti-15Zr-4Nb-4Ta alloy billet forged at Tβ-(30 to 50) °C exhibited high strength and excellent ductility. The effects of forging ratio on mechanical strength and ductility were small at a forging ratio of more than 3. The maximum strength (σmax) markedly increased with decreasing testing temperature below Tβ. The reduction in area (R.A.) value slowly decreased with decreasing testing temperature below Tβ. The temperature dependences of σmax for the Ti-15Zr-4Nb-4Ta and Ti-6Al-4V alloys show the same tendency and might be caused by the temperature difference (ΔT) from Tβ. It was clarified that Ti-15Zr-4Nb-4Ta alloy could be manufactured using the same manufacturing process as for previously approved Ti-6Al-4V alloy, taking into account the difference (ΔT) between Tβ and heat treatment temperature. Also, the manufacturing equivalency of Ti-15Zr-4Nb-4Ta alloy to obtain marketing approval of implants was established. Thus, it was concluded that continuous hot rolling is useful for manufacturing α-β-type Ti alloy.

A novel high speed impact testing method for evaluating the low temperature effects of eutectic and lead‐free solder joints

PurposeThe purpose of this paper is to present a novel high speed impact testing method for evaluating the effects of low temperatures on eutectic and lead‐free solder joints. Interfacial cracking failure of Sn‐based and Pb‐free solders at subzero temperatures is of significant concern for electronic assemblies that operate in harsh environments.Design/methodology/approachThis paper presents a newly designed low temperature control system coupled with an Instron micro‐impact testing machine, which offers a package level test for solder bumps, and that is used at subzero temperature ranges as low as −40°C. This study examined the failure characteristics of 63Sn‐37Pb (Sn37Pb) and 96.5Sn‐3Ag‐0.5Cu (SAC305) solder joints at temperatures ranging from room temperature (R.T.) to −40°C, and at impact speeds of 1 m/s.FindingsThree types of failure mode were identified: M1 interfacial fracture with no residual solder remaining on the pad (interfacial cracking); M2 interfacial fracture with residual solder persisting on the pad (mixed mode failure); and M3 solder ball fracture (bulk solder cracking). The experimental results indicated that the energy to peak load for both types of solders decreased significantly, by approximately 35 percent to 38 percent when the test temperature was reduced from R.T. to −40°C. In addition, the peak load of the Sn37Pb solder joint increased noticeably with a decreasing test temperature. However, the peak load of the SAC305 specimen remained virtually unchanged with a reduction in the temperature. The Sn37Pb solder joints failed in an M3 failure mode under all the considered testing temperatures. The SAC305 solder joints displayed both M1 and M2 failure modes at R.T.; however, they failed almost exclusively in M1 mode at the lowest test temperature of −40°C.Originality/valueThis paper presents a novel technique for evaluating high‐speed impact strength and energy absorbance of Sn‐based and Pb‐free solders at the chip level within a low temperature control system. To overcome the drawbacks experienced in other studies, this study focused specifically on cryo‐impact testing systems and the performed experimental steps to improve the accuracy of post‐test analysis.

Isothermal structure development of Qinghai waxy crude oil after static and dynamic cooling

The isothermal structure development of Qinghai waxy crude oil after static and dynamic cooling has been investigated in detail by using a combination of rheological methods and microscopic observation. Particular attention is paid to the influence of test temperature, cooling rate and shear rate during cooling process. It is observed that for both static and dynamic cooled oils, the structure under isothermal condition always becomes stronger with decreasing test temperature or increasing holding time, while the variation of loss angle are different. For static cooled oil, with a decreasing of cooling rate, the structure increases during the whole holding time, while for the dynamic one, the structure increases first and then decreases. Experiments with a range of shear rates has revealed that, at a fixed cooling rate, the isothermal structure development of waxy crude oil is also strongly influenced by the test temperature. At the test temperature higher than the pour point, higher shear rate can result in stronger structure; while at the temperature approaching pour point, the structure decreases first and then increases with increasing shear rate; at relative lower test temperature, the strength of structure decreases with the increase of shear rate.

Growth of 2 μm Crack-Free GaN on Si(111) Substrates by Metal Organic Chemical Vapor Deposition

A 2 μm high quality crack-free GaN film was successfully grown on 2-inch Si(111) substrates by metal organic chemical vapor deposition with a high temperature AlN/graded-AlGaN multibuffer and an AlN/GaN superlattice interlayer. It is found that the structures, as well as the thicknesses of the multibuffer and interlayer, are crucial for the growth of a crack-free GaN epilayer. The GaN(0002) XRD FWHM of the crack-free sample is 479.8 arcsec, indicating good crystal quality. An AlGaN/GaN heterostructure was grown and tested by Van der Pauw Hall measurement. The electron mobility of two-dimensional electron gas increases from 1928 cm2/V-s to 12277 cm2/V-s when the test-temperature decreases from room temperature to liquid nitrogen temperature. The electron mobility is comparable to that of AlGaN/GaN heterostructures grown on sapphire, and the largest value is obtained for an AlGaN/GaN/Si(111) heterostructure grown by metal organic chemical vapor deposition.

Microstructural evolution and tensile properties of Sn–5Sb solder alloy containing small amount of Ag and Cu

The near peritectic Sn–5Sb Pb-free solder alloy has received considerable attention for high temperature electronic applications, especially on step soldering technology, flip-chip connection. In the present study, a separate addition of the same amount of Ag and Cu are added with the near-peritectic Sn–5Sb solder alloy to investigate the effect of a third element addition on the microstructural, thermal and mechanical properties of the newly developed ternary solder alloys. The results indicate that the melting point of Sn–5Sb solder is enhanced by Ag and Cu additions. Besides, the Ag and Cu content refine the microstructure and form new intermetallic compounds (IMCs) with the near-peritectic Sn–5Sb solder alloy. The tensile tests revealed that all alloys exhibit higher mechanical strength with increasing strain rate and/or decreasing testing temperature, suggesting that the tensile behavior of the three alloys is strain rate and temperature dependence. The yield and ultimate tensile strength are higher for Sn–5Sb–0.7Cu alloy compared with Sn–5Sb and Sn–5Sb–0.7Ag alloys. Good mechanical performance of Sn–5Sb–0.7Cu solder is often correlated to a fine β-Sn grain size and more dispersed Cu-Sn IMC particles, which makes the solder exhibit high strength and yield stress.

Peculiarities of plastic flow involving “deformation waves” observed during low-temperature tensile tests of highly irradiated 12Cr18Ni10Ti and 08Cr16Ni11Mo3 steels

In a previous paper, it was shown that the expectation that neutron irradiation of low-nickel austenitic steels leads to a low saturation level of ductility is not always valid. At high dose ductility is observed first to decrease with dpa during room temperature testing and then under some conditions to increase at higher dose. This produces anomalously high deformation arising from a previously unrecognized mechanism that precludes sustained necking and produces a moving deformation front. It was earlier speculated that this behavior is a result of α-martensite formation in the deforming region. New studies involving testing over −115 to +120 °C confirm that the γ → α transformation is involved with this deformation mechanism and is the cause of the recaptured ductility. When the irradiated alloy has not yet reached the dose threshold of wave initiation at room temperature a decrease in test temperature can induce wave generation, consistent with the known effect of temperature on martensite instability.

Effects of small addition of Ag and/or Cu on the microstructure and properties of Sn–9Zn lead-free solders

In the present study, the effects of separate and dual addition of small amount of Ag and Cu on the microstructure and mechanical properties of the eutectic Sn–9Zn solder alloy were investigated. Results indicate that alloying of Ag and/or Cu resulted in refine the coarse needle-like Zn-rich phase and formation of intermetallic compounds (IMCs) with the eutectic solder. Single addition of Ag led to formation of AgZn, Ag 5Zn 8 and ɛ-AgZn 3 IMCs, which results in significant increase in both ultimate tensile strength (UTS) and ductility, while, the flower shaped and rod shaped Cu 6Sn 5, γ-Cu 5Zn 8 and ɛ-CuZn 5 IMCs produced by Cu alloying, results in small increase in UTS and ductility. The dual addition of Ag and Cu suppressed the appearance of Ag 5Zn 8 IMCs due to the competition for Zn between Cu and Ag, which results in slight decrease in UTS and ductility of Sn–9Zn–1.5Ag solder. Worthy of notice is that all alloys demonstrated an increase in both UTS and yield stress with increasing strain rate and/or decreasing testing temperature, indicating that the tensile behavior of the four alloys often exhibits a strain rate and temperature dependence.

Impact behavior of different stainless steel weldments at low temperatures

A comparative study was made of the fracture behavior of austenitic and duplex stainless steel weldments at cryogenic temperatures by impact testing. The investigated materials were two austenitic (304L and 316L) and one duplex (2505) stainless steel weldments. Shielded metal arc welding (SMAW) and tungsten inert gas welding (TIG) were employed as joining techniques. Instrumented impact testing was performed between room and liquid nitrogen (−196 °C) test temperatures. The results showed a slight decrease in the impact energy of the 304L and 316L base metals with decreasing test temperature. However, their corresponding SMAW and TIG weld metals displayed much greater drop in their impact energy values. A remarkable decrease (higher than 95%) was observed for the duplex stainless steel base and weld metals impact energy with apparent ductile to brittle transition behavior. Examination of fracture surface of tested specimens revealed complete ductile fracture morphology for the austenitic base and weld metals characterized by wide and narrow deep and shallow dimples. On the contrary, the duplex stainless steel base and weld metals fracture surface displayed complete brittle fracture morphology with extended large and small stepped cleavage facets. The ductile and brittle fracture behavior of both austenitic and duplex stainless steels was supplemented by the instrumented load–time traces. The distinct variation in the behavior of the two stainless steel categories was discussed in light of the main parameters that control the deformation mechanisms of stainless steels at low temperatures; stacking fault energy, strain induced martensite transformation and delta ferrite phase deformation.

Performance Evaluation of Resistance Spot Welded Interstitial Free Steel Under Cryogenic Conditions

Abstract Shear tensile (strain rate 102/s) performance of spot welded joints at cryogenic temperatures has been studied considering it as a simple method to indicate the crash resistance performance. The strength of different resistance spot welded joints of interstitial free steel under various heat input conditions has also been evaluated at room temperature for comparison. Micromechanism of fracture of the spot welded joints is investigated by scanning electron microscopy. Although an increase in shear tensile strength with decreasing test temperature is observed in all the spot welds, considerable variations in fracture mode exist in contrast to the room temperature test. The high heat input spot welds remain ductile at all test temperatures, however, low heat input welds become considerably brittle at cryogenic temperatures. Furthermore, medium heat input welds can maintain ductility until 0°C and there is loss of ductility with further lowering of test temperature.

Low-temperature mechanical properties of superconducting radio frequency cavity materials

Low-temperature mechanical behaviors have been investigated for the constituent materials of superconducting radio frequency cavities. Test materials consist of small grain Nb, single crystal Nb, large grain Nb (bicrystal), Ti45Nb–Nb weld joint (e-beam welded), and Ti–316L bimetal joint (explosion welded). The strength of all test metals displayed strong temperature dependence and the Ti–316L bimetal showed the highest strength and lowest ductility among the test materials. The fracture toughness of the small grain Nb metals decreased with decreasing test temperature and reached the lower shelf values (30–40 MPa √m) at or above 173 K. The Ti45Nb base and Ti45Nb–Nb weld metals showed much higher fracture toughness than the small grain Nb. An extrapolation and comparison with existing data showed that the fracture toughness of the small grain Nb metals at 4 K was expected to be similar to those at 173 and 77 K. The results from optical photography at a low magnification and fractography by a scanning electron microscope were consistent with corresponding mechanical properties.

STRESS RELAXATION BEHAVIOR OF IRRADIATED COPPER IN THE TEMPERATURE RANGE 150–300 K

The present study reports the stress relaxation behavior of irradiated polycrystalline 5N copper deformed in the temperature range 150 to 300 K. The wire specimens were exposed to an 18 MeV electron beam at room temperature and stress relaxation tests of the specimens were carried out during the tensile test, using universal testing machine between 150 to 300 K. Stress relaxation rate of the specimens was found to decrease with the decrease of test temperature. The decrease of the stress relaxation rate with temperature in irradiated specimens is attributed to the dislocation-defects interaction, which is more pronounced at low temperature due to the reduction in available thermal energy necessary for the relaxation of dislocations.

Effects of stress and oscillatory frequency on the structural properties of Daqing gelled crude oil at different temperatures

The structural properties of Daqing gelled waxy crude oil were studied with a controlled-stress rheometer under oscillatory shear mode. Our results demonstrate that the gelled waxy crude oil shows viscoelastic properties. The linear viscoelastic region and yielding of crude oil can be determined not only by the critical linear shear stress ( τ cl ) and yield stress ( τ y ), but also by the critical linear shear strain ( γ cl ) and yield strain ( γ y ) respectively. With the decrease of test temperature, τ cl and τ y increased greatly while γ cl and γ y decreased gradually. The crude oil showed more elastic at lower temperatures. The frequency had little effect on the structure of crude oils in the measured range.

Enhanced Tensile Strength and Plasticity of Zr-Cu-Al Bulk Glassy Alloys at Cryogenic Temperatures

No data are available about mechanical behavior of bulk glassy alloys (BGAs) in tension at cryogenic temperatures. In this study, we investigated the effect of temperature on the mechanical behavior of ternary eutectic and hypoeutectic Zr-Cu-Al BGAs fabricated by an arc tilt casting method. Tensile tests were performed for the BGA plates with gauge dimensions of 5 mm in length, 1.2 mm in width and 0.5 mm in thickness at temperatures of 295, 223, 173 and 77 K, at an initial strain rate of 5 10 4 s 1 . Measurements of elastic parameters were also made at temperatures from 97 to 342 K by an ultrasonic pulse method. It is found that the tensile strength and elongation for both BGAs increase with decreasing testing temperature, which is reported for the first time under a tensile condition. At cryogenic temperatures, the tensile elongation of the hypoeutectic Zr59Cu31Al10 BGA tends to be higher than that of the eutectic Zr50Cu40Al10 BGA, although the difference is small. Multiple shear bands are observed on the side surface deformed at lower temperatures. The Young’s and shear moduli, and Debye temperature monotonically increase with decreasing temperature. This indicates that the BGA becomes rigid and the effective atomic distance decreases at cryogenic temperatures, leading to the increase of the tensile strength at cryogenic temperatures. [doi:10.2320/matertrans.M2009186]

The influence of Cu(OH) 2 addition on the low-temperature electrochemical performance of La 0.75Mg 0.25Ni 3.5 hydrogen storage alloy

The influence of Cu(OH) 2 addition in 7 mol/L KOH alkaline electrolyte on the electrochemical properties of La 0.75Mg 0.25Ni 3.5 hydrogen storage alloy electrode was investigated in the testing temperature range of from 25 °C to −40 °C in this paper. XRD Rietveld analyses shows that the La 0.75Mg 0.25Ni 3.5 hydrogen storage alloy consists of LaNi 5 phase, (La, Mg) 2Ni 7 phase and (La,Mg)Ni 3 phase. The maximum discharge capacity and the high-rate dischargeability (HRD) of the La 0.75 Mg 0.25Ni 3.5 alloy electrode both decrease with decreasing testing temperature, which mainly due to the slower hydrogen transfer in the bulk of the alloy and the lower electrocatalytic activity at lower temperatures. The scanning electron microscopy (SEM)/energy dispersive X-ray spectroscopy (EDS) analyses indicate that, with the addition of Cu(OH) 2 to the KOH alkaline electrolyte, fine particles of metal Cu can be coated on the La 0.75Mg 0.25Ni 3.5 alloy electrode surface during charging process by electrodeposition. The Cu powders deposited on the La 0.75Mg 0.25Ni 3.5 alloy electrode can improve the alloy’s low-temperature discharge properties by decreasing its charge-transfer resistance and increasing its exchange current density. The cyclic stability of the Cu-deposited La 0.75Mg 0.25Ni 3.5 alloy electrode can be also improved to a certain extent by increasing its corrosive resistance in KOH alkaline electrolyte.

Thermal-Aware Test Access Mechanism and Wrapper Design Optimization for System-on-Chips

Rapid advances in semiconductor manufacturing technology have led to higher chip power densities, which places greater emphasis on packaging and temperature control during testing. For system-on-chips, peak power-based scheduling algorithms have been used to optimize tests under specified power constraints. However, imposing power constraints does not always solve the problem of overheating due to the non-uniform distribution of power across the chip. This paper presents a TAM/Wrapper co-design methodology for system-on-chips that ensures thermal safety while still optimizing the test schedule. The method combines a simplified thermal-cost model with a traditional bin-packing algorithm to minimize test time while satisfying temperature constraints. Furthermore, for temperature checking, thermal simulation is done using cycle-accurate power profiles for more realistic results. Experiments show that even a minimal sacrifice in test time can yield a considerable decrease in test temperature as well as the possibility of further lowering temperatures beyond those achieved using traditional power-based test scheduling.

Mechanical properties of a Ni 60Pd 20P 17B 3 bulk glassy alloy at cryogenic temperatures

Little is known about mechanical properties of bulk glassy alloys (BGAs) at cryogenic temperatures. In this study, we investigated the effects of temperature and strain rate on the mechanical properties of a Ni 60Pd 20P 17B 3 BGA. Compression tests were performed at temperatures of 295, 223, 173 and 77 K and at strain rates from 5 × 10 −5 to 5 × 10 −3 s −1. Measurements of the elastic parameters were also made at temperatures from 91 to 371 K. It is found that both the maximum compressive stress and plastic strain to failure increase with decreasing testing temperature. The Young and shear moduli, and Debye temperature monotonically increase with decreasing temperature, while Poisson’s ratio decreases, indicating that the BGA becomes rigid and the effective atomic distance decreases at cryogenic temperatures. The mechanism reflecting the changes in the maximum compressive stress and plastic strain with temperature is discussed.