A simple model was developed to predict the impact that solid-state interdiffusion and dissolution have on liquid formation and its duration during transient liquid phase sintering (TLPS). The model predicts that solid-state interdiffusion can dramatically reduce the amount of liquid initially formed during heating. This reduction is dependent on the heating rate and initial base metal particle size. In cases of sintering above the additive phase melting point, the model predicts that base metal dissolution increases liquid phase formation and that this additional melting reduces the base metal particle size. The model predicts that longer times are required to solidify isothermally the greater amounts of liquid formed at higher temperatures (because of dissolution). This agreed qualitatively with experimental results for a Ni-65 wt pct Cu TLPS mixture sintered at 1090°C and 1140°C. Quantitative comparisons between the model and experiment were good at 1140°C; however, the rate of isothermal solidification was underestimated by the model for intermediate sintering times at 1085°C.
Differential scanning calorimetry (DSC) was used to study the transient liquid phase sintering (TLPS) of elemental Ni and Cu powder mixtures. The initial melting behavior, kinetics of isothermal solidification, and remelt behavior of these powder mixtures were quantified, using DSC and metallographic techniques. The effects of the initial liquid distribution and processing temperature on these events were investigated. Quantitative DSC analysis indicates that suppressed liquid fractions form during TLPS at peak temperatures of 1090°C and 1140°C, due to solid-state interdiffusion prior to melting. Larger liquid fractions form at 1140°C compared to 1090°C, due to the recovery of some liquid previously lost to interdiffusion by dissolution at the higher peak temperature. This resulted in higher sintered densities at 1140°C. Complete isothermal solidification of the Cu-rich transient liquid requires more time at 1140°C due to higher liquid fractions initially formed at this temperature compared to those formed at 1090°C. When the initial liquid is distributed nonuniformly, isothermal solidification times are also longer. The DSC and metallographic data indicate that the transient liquid phase (TLP) isothermally solidifies by limited long-range Cu diffusion into the Ni particles and by the epitaxial growth of a surrounding Cu-rich ''layer'' via the gradual outward progression of the solid/liquid interface at compositions given by the liquidus and solidus.
Thermal diffusivity is an important material thermophysical property. The most widely used method for measuring thermal diffusivity is the laser flash technique. In this technique, a sample is placed within a controlled atmosphere furnace and subjected to a finite impulse of radiant energy on its front surface, through the use of a laser. The transport of heat through the sample, as a result of the laser impulse, causes a transient temperature rise on the rear surface of the specimen. This temperature rise is measured by an IR detector placed above the rear sample surface. The net result is a “thermogram” which is a plot of the rear‐face temperature versus time. Assuming a proper set‐up and careful experimentation, the transfer of heat under these conditions approximates one‐dimensional heat flow. Comparing the experimental data with one‐dimensional heat flow theoretical predictions, allows an estimation of thermal diffusivity. There are several methods available to determine thermal diffusivity based on experimental and theoretical comparisons. The simplest method is to determine the “half‐rise time,” t 0.5, which is the time at which the experimentally measured rear‐face temperature reaches half of its maximum value. More accurate methods use sophisticated analysis algorithms to model and fit the entire experimental thermogram curve to an ideal theoretical curve by means of a nonlinear least‐squares procedure. These approaches can include corrections that account for the fact that the experimental measurements only approximate one‐dimensional heat flow conditions. Using the thermogram curve fitting techniques, the measurement of thermal diffusivity of a range of material types including solid thermal insulators and conductors is possible. It is also possible to measure the apparent diffusivity of inhomogeneous samples such as composites and porous materials. Using two‐ and three‐layer analysis methods allows the measurement of thermal diffusivity of liquids. The layer methods can be extended to a determination of the thermal contact resistance of interfaces encountered in coated or bonded materials.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.