Differential Scanning Calorimetry Sample Research Articles

Differential scanning calorimetry of age-hardenable aluminium alloys: effects of sample preparation, experimental conditions, and baseline correction

Precipitation processes in age hardenable aluminium alloys are often investigated by differential scanning calorimetry (DSC). The endothermic and exothermic peaks of the DSC signal correspond to the dissolution and formation of phases, respectively. However, parasitic effects can lead to an unintended curvature of the DSC signal. Although a baseline correction can be used, some imperfections typically remain. Additionally, sample preparation and experimental conditions can influence the precipitation sequence itself and, therefore, the DSC curve. In this study, we investigate the influence of sample preparation by milling and punching on DSC curves for three different aluminium alloys: EN AW-2024, EN AW-6082, and EN AW-7075. Additionally, the influence of quenching and natural ageing was investigated for EN AW-6082. We found that deformation introduced by punching the DSC samples with a piercing die after heat treatment leads to a change in the precipitation kinetics in 2xxx, 6xxx, and 7xxx series alloys. The influence was strongest for punching the samples after solution heat treatment and less significant for punching after artificial ageing. The influence of sample preparation can be avoided by punching the samples before solution heat treatment. If this is not practicable, milling of the samples is a good alternative. The choice of quenching medium and short storage at room temperature before measurement (5 min) had only small effects on the DSC curves. Moreover, the start temperature of the measurement was found to be crucial. For observing phases forming below 100 °C and for low-bias baseline correction, the measurement should start at low-temperatures (i.e. ∼\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim$$\\end{document} − 50 °C).

Removal of Iron from a Secondary Al–Si Die‐Casting Alloy by Metal Melt Filtration in a Laboratory Filtration Apparatus

The influence of chemical composition and cooling rate is investigated on a secondary die‐casting alloy with the aim of reduction of iron using metal melt filtration in a specially developed laboratory filtration apparatus. Based on the defined thermal conditions of the device, differential scanning calorimetry (DSC) cooling curves are determined to obtain formation temperatures of the primary iron‐containing intermetallic phases (also called sludge phases) for an EN AC‐AlSi9Cu3(Fe) alloy with different contents of Fe, Mn, and Cr. The DSC samples are then analyzed metallographically, and the results are compared with CalPhaD calculations. After that, the temperature of the sludge formation is adjusted using furnace‐operating curves to confirm the presence of the intermetallic phases by sedimentation and filtration trials. The Fe content is reduced by about 50%, as shown by chemical analysis based on remelted materials in optical emission spectroscopy. The elements Mn and Cr decrease by ≈66% and 86% after filtration at 620 °C, respectively.

DSC Assessment on Curing Degree of Micron-scaled Adhesive Layer in Lamination-pressed Flexible Printed Circuit Panels

Continuous monitoring and optimisation of the lamination process are critical in negating flexible printed circuit (FPC) delamination risk during operation. The main QC inspection criterion of the lamination adhesive’s curing degree is adhesive thickness. However, this method is prone to measurement error due to poor microscopy image definition and the inspector’s measurement parallax error. The feasibility of using thermal characterisation to measure the difference in curing degrees of micron-scaled adhesive layer of laminated FPC was investigated. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used according to IPC standards. Polyimide-epoxy adhesive coverlays were laminated onto both sides of FPC at 120 kgf/cm2 pressure and 180 °C temperature for 120 s. Then, the coverlays were subjected to oven curing at 150 °C for 60 min. The DSC detected a small difference in the curing degree of adhesive layers in the two cured FPC laminated in different laminating-press openings (T1 and T2). T2 had a glass transition temperature (Tg) of 106.5 °C, which was higher than that for T1 (105 °C), thereby suggesting that the former had a higher curing degree than the latter. This result was consistent with the adhesive thickness measurement result of the DSC samples. The adhesive thickness of T2 was smaller (30.97 µm) than that of the T1 (31.76 µm). T2 had a higher curing degree than T1 because of the larger shrinkage percentage. In comparison with DSC, TGA was unable to detect the curing degree difference between the samples because of the undetected weight loss resulting from the adhesive curing.

Pyrolysis Kinetics and Flammability Evaluation of Rigid Polyurethane with Different Isocyanate Content

Polyurethane (PU) is a typical product of the reaction between isocyanate and polyol, whose ratio would greatly influence material properties. In this paper, to investigate the influence of isocyanate on PU thermal stability and flammability, three kinds of rigid polyurethanes (RPUs) with different isocyanate ratio (1.05, 1.1, and 2.0) were manufactured in a laboratory and employed to have a series of TG (thermogravimetry), DSC (differential scanning calorimetry), and cone calorimetry tests. Kissinger’s method was used to calculate the activation energy and judge their stabilities. However, for such a complex degradation which consists of five reactions, it does not make sense by Kissinger method to obtain only two peak active energies. Considering complexity of PU degradation in air, genetic algorithm (GA) was employed to calculate kinetic triplets of five sub-reactions. The effects of isocyanate contents on each sub-reaction stability were obtained and then analyzed. By cone calorimeter testing, we found that great differences in heat release rate data. However, DSC analysis showed a complete opposite changed trend. Such difference is caused by DSC and calorimeter’s sample morphology, the former using grinded polyurethane powders but the latter polyurethane foam block.

DSC and microstructure analysis of high temperature Ni-Ti-Hf, low hysteresis Ni-Ti-Cu and conventional super-elastic and shape memory Ni-Ti alloy ingots and wires

The progression of martensitic transformations in calorimetric experiments on NiTi-based shape memory alloys (SMA) depends significantly on the material composition, processing history and the thermo-mechanical treatment which is performed to prepare the material for use in application. The phase transformations in Ni-Ti alloys are first order transitions, i.e. the microstructure symmetry changes occur spontaneously and superheating and supercooling effects emerge. Thus, the thermal scanning rate in differential scanning calorimetry (DSC) affects the observation of important material parameters for the characterization of shape memory alloys like onset temperatures, hysteresis width and change in enthalpy of phase transformations. This work depicts how the transformation characteristics as observed by DSC measurements vary significantly by altering the alloy composition and processing conditions of the material. An in-depth calorimetric study on a wide range of NiTi-based alloys which were prepared as heat treated ingot and processed wire was performed. In order to evaluate also the rate effect on the transformation of distinct alloys, DSC rates from 1 to 30 °C/min were tested, highlighting the interplay between thermal scanning velocity and material parameters. Manifold results are presented on how chemistry, microstructure, DSC sample geometry and processing stresses in the materials contribute to award the alloys diverging sensitivity to the thermal scanning rate. Deviations in binary Ni-Ti composition alter the sensitivity to heating and cooling rate, e.g. martensitic transformation in annealed super-elastic (SE) wire is stronger affected by the rate than shape memory wire due to differences in the precipitation behavior. Ni-Ti-Hf high temperature shape memory alloys show a rather small enlargement of hysteresis, but a huge shift in transformation temperatures, while Cu addition to Ni-Ti causes very sensitive hysteresis changes up on modifying thermal rates which is assigned to B19 orthorhombic transformation. Transformation parameters of wires are less affected by DSC rates than ingots due to their high surface to volume ratio, while sample weight and surface finish is observed to have a minor impact. Small grains and residual strains owing to processing history of drawn wire tend to stabilize the transformation. In materials which exhibit R-phase transformation, the low heat capacity of this phase could be responsible for its minor sensitivity to variations in DSC rate.

Enthalpy-temperature plots to compare calorimetric measurements of phase change materials at different sample scales

Phase change materials (PCM) can provide high thermal energy storage capacities in narrow temperature ranges around their phase change temperature. The expectable maximum storage capacity of a PCM in a defined temperature range is equal to the enthalpy change in that range and can be determined via calorimetric measurements such as differential scanning calorimetry (DSC) or T-History calorimetry. T-History samples (∼15 ml) are about 1000 times larger than DSC samples (∼15 μl). Experiments in a pilot plant are performed to study the charging and discharging behaviour of even larger amounts of the PCM (∼150 l). The common practise is to investigate PCM at one scale, rarely at two scales. In this work, the characterisation was carried out at three scales (DSC, T-History, and pilot plant) for four PCM (RT58, bischofite, d-mannitol, and hydroquinone). Thereby, the question arises how the enthalpy changes measured at different scales and under different conditions can be compared. In literature, the melting enthalpy is usually assigned to a single temperature without indicating the temperature range considered for evaluation. In very few instances, the enthalpy change within a defined temperature range is stated. In both cases, results measured under different conditions are difficult to compare. In this work, it is demonstrated that enthalpy-temperature plots facilitate the comparison and interpretation of measurements obtained under different experimental methods at different sample scales.

Influence of Surface Crystalline Structures on DSC Analysis of PTFE

The physical and mechanical properties of polytetrafluorethylene (PTFE) are greatly dependent on the degree of crystallinity and this is extremely important for the modeling of PTFE processing which is complex and costly. Differential scanning calorimetry (DSC) is one of the most important techniques for the determination of the degree of crystallinity and powder granules of the sample are generally used in the analysis. This procedure provides samples with a high surface-to-volume ratio, resulting in the formation of a considerable number of surface crystalline structures, called warts, along with the bulk crystallization, as shown by scanning electron microscopy. The presence of warts has a significant effect on the PTFE melting enthalpy and thus hinders the correct estimation of the degree of crystallinity of industrial PTFE parts, in which bulk crystallization prevails. In this study, we propose a procedure which does not lead to the formation of warts in the DSC sample and thus allows a more accurate determination of the melting enthalpy (or the degree of crystallinity) of industrial PTFE parts. We demonstrate that samples must be extracted from the core of dense (well-pressed) parts previously sintered in an oven, and the use of powder granules and/or sintering in DSC is not recommended.Keywords:

Analysis of aluminium brazing sheet differential scanning calorimetry data

Differential scanning calorimetry (DSC) measurements have provided insight into metallurgical reactions which can occur during joining of Al brazing sheet. Researchers have claimed that DSC is sensitive enough to differentiate between brazing sheets with different initial conditions; however, no rigorous proof of this claim has been given. The sensitivity of DSC measurements, as measured by changes in melting peak area, to experimental factors such as DSC sample preparation, sample orientation during testing and starting sheet temper has been investigated. A 23 factorial design was used, and the results were analysed using analysis of variance. The results showed that only the sheet punching direction during sample preparation had a statistically significant influence on the DSC measurements. Microstructure analysis revealed that punching on the core layer of the sheet led to extra clad alloy on the side of the sample, which melted during heating and contributed to a greater measured melting peak area.

Thermodynamic properties and phase transitions of ternary Co–Cu–Si alloys with equiatomic Co/Cu ratio

Different amounts of Si element were introduced into binary Co50Cu50 alloy to investigate the thermodynamic properties and phase transitions of ternary Co50−x/2Cu50−x/2Six (x = 10, 20, 30, 40 and 50 at%) alloys. Their liquidus and solidus temperatures versus Si content were determined by the differential scanning calorimetry (DSC) method. It was found that the addition of Si element depressed both the liquidus and solidus temperatures as compared with binary Co50Cu50 alloy. In particular, the additions of 10 and 20 at% Si remarkably reduced the critical undercooling for liquid demixing to only 3 and 1 K, whereas no liquid phase separation took place in other Co50−x/2Cu50−x/2Six alloys. The relationship between the enthalpy of fusion and alloy composition was also established by a polynomial function on the basis of the measured data. The solidification microstructures of the DSC samples were investigated corresponding to the calorimetric signals, based on which the solidification pathway for each Co50−x/2Cu50−x/2Six alloy was elucidated. The Si element displays stronger affinity with the Co element than the Cu element. As Si content rises, the pseudobinary eutectic (Co + Co2Si), (Co2Si + CoSi), (CoSi + CoSi2) and (Cu3Si + Si) structures were successively formed, and there were no ternary intermetallic compounds in these alloys. The thermal diffusivity of solid ternary Co50−x/2Cu50−x/2Six alloys was determined by a laser flash method in a wide temperature range from 300 to 1180 K, which showed a decreasing tendency with the increase of Si content.

Enhanced Thermal Stability of Si/Graphene Composite Anode in the Presence of Fluoroethylene Carbonate Additive

Silicon-based materials are becoming very promising next generation anode materials for lithium ion battery application after intensive research efforts (1-2), which address the volume expansion by new material development, solid electrolyte interface (SEI) formation by introducing additive(4), and electrode integrity by choosing appropriate binders (3). However, compared to electrochemical performance of silicon based electrode, thermal characteristics of silicon composite material has not been fully illustrated. In this study, we carried out differential scanning calorimetry (DSC) experiments on lithiated Si/graphene composite electrode in carbonate electrolyte with fluoroethylene carbonate (FEC) as additive. Series electrolytes with various FEC concentration (0, 5, 10 and 20 wt%) were prepared using 1.2M LiPF6 in EC/EMC (3/7, by wt) electrolyte. Electrodes were prepared by casting the mixture of Si/graphene composite material (XG sciences), graphene (XG sciences) and poly acrylic acid (PAA) on copper foil. All electrodes had been cycled for three cycles, and then lithiated to various lithiation states. The samples were then sealed in the DSC sample holder with additional electrolyte and tested using Pyris 1 DSC (Perkin Elmer). The test results are shown in Fig. 1. It is very clear from DSC results that FEC additive play an important role to the thermal stability of the silicon based electrode. When there is no FEC additive, the on-set temperature for exothermic reaction is lower than that with FEC. The exothermic reaction at lower temperature is related to the breakdown of SEI layer with electrolyte (5-7). The less exothermic reaction of silicon composite electrodes with FEC indicates that the better thermal stability of SEI is formed by FEC additive. In this work, the thermal effect of both FEC concentration and the state of lithiation in the silicon composite electrode will also be presented. Acknowledgement The silicon material is provided by XG sciences. The validation was conducted under Cell Analysis, Modeling, and Prototyping (CAMP) Facility at ANL. Support from David Howell and Peter Faguy of the U.S. Department of Energy’s Office of Vehicle Technologies is gratefully acknowledged.

Evaluation of aluminosilicate glass sintering during differential scanning calorimetry

The aim of this work is to investigate a difference in heat flow observed in the differential scanning calorimetry curves when aluminosilicate glasses are analyzed. Glasses with nominal composition 56.21 SiO2 18.65 Al2O3 25.14 MgO (wt%) were produced by the conventional melting process. Glass frits were milled and sieved in the range of 45–63µm. The material was analyzed by X-ray fluorescence spectrometry, X-ray diffraction, differential scanning calorimetry (DSC), and differential thermal analyses (DTA). The particle size distribution was determined by laser diffraction technique. The microstructures of the samples were observed by scanning electron microscopy after removing them from the DSC sample holder. The density was determined by He picnometry. The difference in heat flow in the DSC curves is assigned to the sintering process occurring during the heating cycle, which was confirmed by the neck formation in the particle interface, DSC signal variation in isothermal measurements, no change in the heat flow when monolith specimen are analyzed, and in subsequent DSC analysis after cooling. The concurrent crystallization was also determined.

Nucleation and Growth of Cu-Al Intermetallics in Al-Modified Sn-Cu and Sn-Ag-Cu Lead-Free Solder Alloys

Lead-free solder alloys Sn-Cu (SC) and Sn-Ag-Cu (SAC) are widely used by the microelectronics industry, but enhanced control of the microstructure is needed to improve solder performance. For such control, nucleation and stability of Cu-Al intermetallic compound (IMC) solidification catalysts were investigated by variation of the Cu (0.7–3.0 wt.%) and Al (0.0–0.4 wt.%) content of SC + Al and SAC + Al alloys, and of SAC + Al ball-grid array (BGA) solder joints. All of the Al-modified alloys produced Cu-Al IMC particles with different morphologies and phases (occasionally non-equilibrium phases). A trend of increasing Cu-Al IMC volume fraction with increasing Al content was established. Because of solidification of non-equilibrium phases in wire alloy structures, differential scanning calorimetry (DSC) experiments revealed delayed, non-equilibrium melting at high temperatures related to quenched-in Cu-Al phases; a final liquidus of 960–1200°C was recorded. During cooling from 1200°C, the DSC samples had the solidification behavior expected from thermodynamic equilibrium calculations. Solidification of the ternary alloys commenced with formation of ternary β and Cu-Al δ phases at 450–550°C; this was followed by β-Sn, and, finally, Cu6Sn5 and Cu-Al γ1. Because of the presence of the retained, high-temperature phases in the alloys, particle size and volume fraction of the room temperature Cu-Al IMC phases were observed to increase when the alloy casting temperature was reduced from 1200°C to 800°C, even though both temperatures are above the calculated liquidus temperature of the alloys. Preliminary electron backscatter diffraction results seemed to show Sn grain refinement in the SAC + Al BGA alloy.

The effect of temperature gradients on the parameters of Adam–Gibbs model

The most commonly used method for studying relaxation processes in polymers is monitoring the enthalpy recovery by measuring differential scanning calorimetry (DSC) heat capacity data. Because of its great influence on heat capacity data, the effect of temperature gradients in the sample on relaxation dynamics study should be investigated. A model for calculating temperature profile in a DSC sample was proposed previously by combining Fourier's law of heat conduction with the Tool–Narayanaswamy–Moynihan (TNM) model. This model was examined using PS samples with different thicknesses. It was found that the temperature gradient influenced optimized values of the kinetic parameters. The thermal history dependence of model parameters is still prominent, however. Here the Scherer–Hodge (SH) equation (based on the Adam–Gibbs model) instead of the TNM equation, is used for describing the relaxation time–structure–temperature relationship in the temperature profile calculation. It is found that the influence of temperature gradients on the thermal history dependence of the Adam–Gibbs (AG) model parameters is greater than that of the TNM model parameters. But the thermal history dependence of the AG model parameters still exists when the thermal lag effect was incorporated.

Thermal transitions of gelatin evaluated using DSC sample pans of various seal integrities

Differential scanning calorimetry (DSC) has become a popular tool to investigate thermal transitions in food ingredients such as gelatin. Upon heating commercial gelatin samples beyond glass transition (Tg) and melting (Tm) temperatures, a relatively large endothermic transition (Ti) can be observed. We have observed that both the peak temperature and the enthalpy of the Ti transition are influenced by the integrity of the seal of the DSC pans used for the analysis. This study shows that escape of moisture from the DSC pan appears to be responsible for this effect. The effect of different types of DSC pans, as well as technique of sealing them on the Ti transition were evaluated using DSC, SDT, and TG–MS.

Anisothermal solid-state reactions of Ni/Al nanometric multilayers

The structural evolution of Ni/Al multilayer thin films with temperature was studied by differential scanning calorimetry (DSC), scanning electron microscopy (SEM), transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM) and X-ray diffraction (XRD). Thin films with nanometric Ni and Al alternated layers were deposited by d.c. magnetron sputtering. In our experiments, we used a bilayer thickness of 5, 14 and 30 nm and a total film thickness ranging from 2 to 2.7 μm. The XRD patterns of the as-deposited sample revealed only peaks of Al and Ni. DSC experiments were performed on freestanding films, from room temperature to 700 °C at 10 and 40 °C/min. Two exothermic reactions were detected in the DSC curves of the film with a 30 nm bilayer thickness, with peak temperatures at 230 and 330 °C. The films with 5 and 14 nm bilayer thickness presented only one exothermic peak at 190 and 250 °C, respectively. To identify the intermetallic reaction products, DSC samples were examined by XRD. NiAl formation corresponds to one single DSC peak, for films with short bilayer thicknesses (5 and 14 nm). The films with 30 nm bilayer thickness were heated at 250 °C ( T = T 1st peak), 300 °C ( T 1st peak < T < T 2nd peak), 450 °C ( T > T 2nd peak) and 700 °C. The XRD results indicated that at 250 °C the phase formed was NiAl 3, whilst NiAl 3 and Ni 2Al 3 phases were identified at 300 °C. For the 450 °C sample, only NiAl was detected. Further heating to 700 °C promotes the growth of NiAl grains.

Study on gluing reaction between WPI adhesive and bamboo by means of DSC

PurposeThe purpose of this paper is to study interactions between water‐based polymer isocyanate (WPI) adhesive and bamboo by means of differential scanning calorimetry (DSC).Design/methodology/approachThe method of adapting new reference substance replacing aluminium was used due to the special characteristic of WPI adhesive when studying reactions between WPI adhesive and bamboo.FindingsThe methods of changing reference substance could counteract effect of water in the sample on DSC measurement. The results of DSC analysis showed that hardener of WPI adhesive can react with water and also with ‐OH in bamboo and matrix of WPI adhesives. That is to say that a competition exists between urethane formation (covalent bonding of isocyanate with hydroxyl groups in bamboo and matrix in WPI adhesive) and urea formation (isocyanate consumption due to the reaction with water) during the operation of glued bamboo products.Research limitations/implicationsThe method of changing reference substance can be used for other DSC samples in which water cannot be conveniently removed, but this method requires that weight of reference substance to be exactly the same as the sample used in DSC measurement. So accuracy of weighing was very important in this DSC measurement.Practical implicationsThe method developed in this paper provides a simple and practical solution to studying interactions between WPI adhesive and bamboo by means of DSC.Originality/valueChanging reference substance was brought forward as a new method of counteracting effect of water in the sample on DSC measurement. The understanding gained through this study could help improve bonding properties of glued bamboo products.

Stabilization of Na,K–ATPase by ionic interactions

The effect of ions on the thermostability and unfolding of Na,K–ATPase from shark salt gland was studied and compared with that of Na,K–ATPase from pig kidney by using differential scanning calorimetry (DSC) and activity assays. In 1 mM histidine at pH 7, the shark enzyme inactivates rapidly at 20 °C, as does the kidney enzyme at 42 °C (but not at 20 °C). Increasing ionic strength by addition of 20 mM histidine, or of 1 mM NaCl or KCl, protects both enzymes against this rapid inactivation. As detected by DSC, the shark enzyme undergoes thermal unfolding at lower temperature ( T m ≈ 45 °C) than does the kidney enzyme ( T m ≈ 55 °C). Both calorimetric endotherms indicate multi-step unfolding, probably associated with different cooperative domains. Whereas the overall heat of unfolding is similar for the kidney enzyme in either 1 mM or 20 mM histidine, components with high mid-point temperatures are lost from the unfolding transition of the shark enzyme in 1 mM histidine, relative to that in 20 mM histidine. This is attributed to partial unfolding of the enzyme due to a high hydrostatic pressure during centrifugation of DSC samples at low ionic strength, which correlates with inactivation measurements. Addition of 10 mM NaCl to shark enzyme in 1 mM histidine protects against inactivation during centrifugation of the DSC sample, but incubation for 1 h at 20 °C prior to addition of NaCl results in loss of components with lower mid-point temperatures within the unfolding transition. Cations at millimolar concentration therefore afford at least two distinct modes of stabilization, likely affecting separate cooperative domains. The different thermal stabilities and denaturation temperatures of the two Na,K–ATPases correlate with the respective physiological temperatures, and may be attributed to the different lipid environments.

Correction of melting peaks of different PE grades accounting for heat transfer in DSC samples

In this work, the effect of heat transfer on the apparent melting behavior of linear low-density polyethylene (LLDPE) and recycled high-density polyethylene (rHDPE) was studied. Experimental melting temperature distributions (MTD) were shown to be significantly affected by the heating rate of the scan and the sample mass. The sample mass dependence of the MTD is attributed to thermal inertia of differential scanning calorimetry (DSC) samples. On the other hand, the heating rate dependence of MTD is in apparent contrast with the thermodynamic nature of the melting process. The existence of temperature gradients, responsible for heat transfer in DSC samples, was explained by adimensional analysis and evaluation of the Biot and Deborah numbers. A previously introduced equation was used to model melting behavior of the polymers. The parameters from non-linear regression were shown to be dependent on the product between the scanning rate and the square of sample mass. Regression parameters were extrapolated at infinite Deborah number. The MTD obtained at infinite Deborah number was considered the real MTD of the polymer, and was coupled with a heat transfer model to calculate the actual temperature of the sample. The local rate of heating, multiplied by the true MTD, provided the local rate of melting. The average rate of melting was compared with the experimental DSC signal. The very close agreement of the experimental and numerical prediction results evidence that the observed differences between melting curves obtained at different heating rates and sample mass can be attributed to thermal gradients in the DSC sample.

A study of transient liquid-phase bonding of Ag-Cu using differential scanning calorimetry

A novel approach using differential scanning calorimetry (DSC) to quantify interface kinetics in a solid/liquid diffusion couple is applied to characterize the isothermal solidification stage during transient liquid-phase (TLP) bonding of Ag and Cu using a Ag-Cu interlayer. When the DSC results are properly interpreted, the measured interface kinetics are more accurate than those obtained using traditional metallographic techniques. Experimental results are compared to predictions for isothermal solidification given by a selection of analytical models. The comparison yields close agreement with a solution that assumes a moving boundary; but accuracy of the predictions is very sensitive to selection of solute diffusivity. Metallographic inspection of the DSC samples and traditional TLP bonds validates the kinetics measured using this technique, and supports the prediction given by the analytical model. This study shows that the method of using DSC to quantify interface kinetics is valuable in the refinement of process parameters for TLP bonding. Furthermore, simple analytical solutions can be applied to predict the process kinetics of isothermal solidification in simple binary systems with considerable accuracy when the effects of grain boundaries can be neglected, thus reducing the need for complex numerical models when developing process parameters.

Shape memory characteristics of TiNi casting alloys made by using self-propagating high-temperature synthesis

Self-propagating high-temperature synthesis (SHS) is a new method of making an ingot of TiNi. This method shows little gravity segregation. The purpose of this study is to investigate the difference of the shape memory characteristics of the TiNi casting alloys made from a SHS ingot and from a conventional melt cast ingot. The samples used in this study were rods made by centrifugal casting. Differential scanning calorimetry (DSC), X-ray diffraction, and tensile test were used to examine the shape memory characteristics on the samples. The heat treatment conditions were 773 K–1.8 ks and 1073 K–3.6 ks, respectively. The DSC samples were both ends (the top and bottom area) of the rod samples. The results of the XRD measurements showed that TiNi phase was obtained in all the samples. In contrast, the result of the DSC test showed that more gravity segregation effect happened in the melt cast sample than in the SHS sample. As the conclusion of this study, gravity segregation had little effect in the SHS ingot sample.