Dilatometry Analysis Research Articles

Phase transformations in PuGa 1at.% alloy: Study of whole reversion process following martensitic transformation

Abstract The purpose of this work was to study PuGa 1 at.% alloy behavior from martensitic transformation to the whole reversion process. The relevant phase transformations were investigated as a function of temperature via in situ X-ray diffraction and dilatometry analyses carried out at low and high temperatures. The results show that the δ-to-α′ martensitic transformation occurring at low temperatures is direct and does not involve any intermediate γ′ phase. They also reveal that the reverse transformation of the two-phase δ + α′ alloy during heating involves two competing modes, namely direct and indirect reversion. The latter is associated with a Ga diffusion process that governs the ratio between these reversion modes. More precisely, our study demonstrates that the indirect reversion process consists of a Ga-enrichment of the remaining δ phase as well as the emergence of the β and γ phases of pure plutonium. Every stage of indirect reversion has been discussed in relation to the equilibrium phase diagram of the Pu–Ga binary system.

Typical problems in push-rod dilatometry analysis

Typical problems in push-rod dilatometry analysis

Dilatometric Characterization of Foundry Sands

Dilatometric Characterization of Foundry Sands The goal of this contribution is summary of physical - chemistry properties of usually used foundry silica and no - silica sands in Czech foundries. With the help of dilatometry analysis theoretical assumptions of influence of grain shape and size on dilatation value of sands were confirmed. Determined was the possibility of dilatometry analysis employment for preparing special (hybrid) sands with lower and/or more linear character of dilatation.

Kinetic Study of the Austempering Reactions in Ductile Irons

Kinetics of the reaction that occur during the austempering heat treatment in unalloyed and alloyed ductile irons with 1Cu-0.25Mo, 1Ni-0.25Mo, and 0.7Cu-1Ni-0.25Mo, was studied. The austenitization and austempering cycles were achieved by isothermal dilatometry in cylindrical samples of 2 mm in diameter and 12 mm in length. The specimens were austenitized at 870 °C for 120 min, followed by isothermal holding for 300 min at temperatures between 270 and 420 °C. Kinetic parameters such as the order of reaction “n” and the rate of reaction “k” were calculated using the Johnson-Mehl equation while the empirical activation energy was calculated by means of the Arrhenius equation. It was found that the values of “k” decreased with the addition of Cu, Ni, and Mo as well as with the reduction of the isothermal temperature. The activation energy changes with the austempering temperature, in the range 30,348-58,250 J/mol when the heat treatment was carried out between 370 and 420 °C and 10,336-26,683 J/mol when the temperature varied from 270 to 350 °C. The microstructures in samples austempered at 370 and 315 °C were observed by transmission electron microscopy. No carbides precipitation was observed on samples heat treated at 370 °C for less than 120 min, while at 315 °C carbides of hexagonal structure e(Fe2.4C) were found from the beginning of the transformation. The smallest value of activation energy and a slower kinetic transformation seem to be related with the presence of a carbide phase. Additionally, the time results obtained for transformation fractions of 0.05 and 0.95 by the dilatometry analysis were used to build the temperature-time-transformation diagrams for the irons.

Kinetics of orthorhombic martensite decomposition in TC21 alloy under isothermal conditions

The kinetics of martensite decomposition in TC21 alloy was investigated at isothermal conditions in the temperature range 500–850 °C. The dilatometry technique was utilized to trace the transformation process for different aging temperatures. Within the framework of the Avrami theory, the analysis of the experimental data was made by means of the Johnson–Mehl–Avrami (JMA) equation. A very good correspondence between the calculated and the experimental results was found. The JMA kinetic parameters obtained from different aging temperatures implied different mechanisms of the transformation. The α″ phase transforms to α + α″ (rich) at 500 °C and the transformation is incomplete. Further increase of the temperature to 800 and 850 °C results in directly transformation α″ →α + β. The mechanism of the transformation alters during the course of the transformation for 550, 600, 650, 700, and 750 °C. Moreover, The TTT diagram was constructed for the martensite decomposition in TC21 alloy based on the dilatometry analysis and JMA theory, respectively. Good agreement between experimental and calculated TTT diagram is observed.

Internal Friction on AISI 304 Stainless Steels with Low Tensile Deformations at Temperatures between−50 and 20C

Austenitic stainless steels specimens were deformed by tension in temperatures in the range of−50Cto 20Cand 0.03 to 0.12 true strain, in order to obtain different volumetric fractions ofε(hexagonal close packed) andα′(body centered cubic) strain induced martensites. The morphology, distribution and volumetric fractions of the martensites were characterized by metallography and dilatometry analysis and quantified by ferrite detector measurements. The damping behavior of specimens with different volumetric fractions of martensites was studied in an inverted torsion pendulum in the 40Cto 400Crange. Theε- andα′-martensites reversion was observed in the temperature range of 50C–200Cand 500C–800C, respectively, by dilatometry. Internal friction curves in function of temperature of the deformed samples presented internal friction peaks. The first internal friction peak is related to sum of the amount ofε- andα′-martensites. For low deformations it aligns around 130Cand it is related only to theε→γreverse transformation. The peak situated around 350Cincreases with the specimen degree of deformation and is, probably, related to the presence ofα′/γinterfaces, and deformed austenite.

Descriptive microstructure and fracture surface observations of fired volcanic ash

Crystals of the pyroxene group (diopside, augite and enstatite, hedenbergite), series of crystals with the general formula (Mg x Fe1–x )2SiO4 having various geometry, identified as spinel (and olivine), and plagioclase crystals from anorthite to anorthoclase that grow together in mass having thin parallel groves embedded in a complex matrix together with calcium alumina silicate grains were found to be the descriptive microstructure of fired volcanic ash. Quartz grains were rarely present as confirmed by dilatometry analysis, XRD, SEM and DTA. The presence of dendrites continuously growing to pyroxene crystals indicated the precipitation/crystallization of these crystals from matrix and regions of glass concentration enhance by ions diffusion. Rings of Ti-rich iron micro-crystals observed around spinel (and olivine) suggested the probable nucleating role of these micro-crystals for the precipitation/crystallization phenomenon. The various types of crystals formed, the difference in their geometry and size and their interlocking mechanism result in a contiguous and dense structure with relevant characteristics at relative low temperature (1125–1150 °C) confirming volcanic ash as a promising alternative raw material for vitrified ceramic products. It was concluded that controlled precipitation/crystallization of raw volcanic ash results on microstructure similar to that of glass-ceramic materials. The observation of fracture surface allowed comparison of fracture mechanics of volcanic ash ceramic to that of conventional vitrified ceramics.

A Mexican kaolin deposit: XANES characterization, mineralogical phase analysis and applications

A kaolin obtained from Villa de Reyes, a region near to San Luis Potosi (Mexico) was characterized by means of X-ray powder diffraction (XRD, optical microscopy (OM), scanning electron microscopy (SEM), X-ray fluorescence (XRF), X-Ray Absorption Near Edge Spectroscopy (XANES), thermal analysis (DTA/TGA), dilatometry (DIL), and chemical analysis. Mineralogical and morphological characteristics of the mineral are presented. The kaolin sample was formed mainly by kaolinite, but other minor phases were also detected such as quartz, cristobalite, tridymite, and dolomite. The high content of volcanic glass detected, by optical microscopy, revealed an incomplete kaolinization process of the raw material. The reddish color of the kaolin was associated with the free iron content in the form of limonite [FeO(OH)], which was determined by XANES. The influence of the particle size on the whiteness of kaolin was evaluated. Dilatometric analysis revealed a strong thermal expansion between 110 y 240 °C, which would difficult the use of this material in traditional ceramic applications. On the other hand the presence of glass and high temperature phases of SiO2, such as cristobalite and tridymite will favor its use in the cement industry.

Study of the age-hardening in an Au-Cu-Ag dental alloy with Pt and Pd additions with dilatometry, hardness measurements and microstructural analysis

The age-hardening behaviour in a commercial gold dental alloy based on the Au-Cu-Ag system with platinum and palladium addition has been investigated with light optical microscope, scanning electron microscope, EDXS, image analysis, hardness measurements and dilatometric tests. The dilatometer, although seldom used in studying the hardening of precious alloys has proved useful to give good information on the heat treatment parameters. The most important hardening of the homogenised alloy takes place after isothermal treatments at temperatures between 150°C and 350°C. The metallographic analysis has shown that the microstructure is modified with the presence of discontinuous precipitation on the grain boundaries only after treatments at temperatures starting from 260°C.

An investigation of co-fired varistor-NiZn ferrite multilayers

The co-firing characteristics of ZnO varistor and NiZn ferrite thick films were investigated, the objective being to create an integrated passive device. Bismuth oxide additions were used to increase the shrinkage of the ferrite during sintering. Dilatometry analysis proved that well-matched shrinkage characteristics could be obtained for bismuth oxide-modified ferrite compositions and the starting varistor material. Cross-boundary diffusion across the co-fired varistor–ferrite interface occurred during sintering, but application of a barrier layer of pure zinc oxide reduced this phenomenon considerably. By tailoring the shrinkage, strong, crack-free co-fired layers with no evidence of cracking or delamination were obtained. No deleterious effects were observed due to electroding of the varistor and ferrite materials.

Contribution to porous mullite synthesis from clays by adding Al and Mg powders

This work has been undertaken to consider the production of porous mullite from kaolinitic clays. X-ray diffraction, scanning electron microscopy, thermogravimetry, differential thermal and dilatometry analyses were performed to study their thermal behavior. Pure and porous mullite was obtained by adding aluminum metal powder to kaolinite and hot processing in oxidizing atmosphere. Comparative studies were carried out to evaluate the influence of various weight ratios of magnesium on both the formation and reactive sintering of mullite. Porosity was shown to be increased with magnesium content while needle-like mullite crystals could be observed.

Development of a dual phase steel using orthogonal design method

A 50 kg-grade cold rolled dual phase (DP) steel was developed based on the orthogonal design method. The intercritical annealing, aging and galvanizing temperatures during the heat treatment were considered as controllable factors and three levels for each of these factors were selected. The optimal experimental conditions were acquired by the analysis of variance (ANOVA) on the ultimate tensile strength (UTS) and the total elongation of the DP steel. A dilatometry analysis was performed to measure the phase transformation kinetics of the DP steel and to verify the statistically analyzed results. These metallurgical observations explained well the statistically analyzed results.

Sintering and characterisation of nano-sized yttria-stabilised zirconia

Two types of commercially available nano-sized, ZrO2?3mol%Y2O3 (Y-Tetragonal Zirconia Polycrystals (TZP)) powders were investigated. BET surface area analysis showed the powders to be nano-sized as determined using Equivalent Spherical Diameter (ESDBET) theory. Dilatometry analysis showed that one of the powders underwent complete shrinkage during isothermal sintering; the other did not. The point of maximum densification rate for the powders differed by approximately 100?C. A dramatic expansion associated with the tetragonal to monoclinic transformation was observed by dilatometry for unstabilised zirconia, but not for TZP samples. X-ray diffraction showed that the starting TZP powders contained some monoclinic zirconia, but confirmed that discs sintered from this powder were wholly tetragonal. For one powder type, the fracture toughness of discs decreased almost linearly with increasing sintering temperature, whereas for the other the fracture toughness was relatively stable across the temperature range. Two-step sintering enabled a maximum fracture toughness of 6.12 MPa m1/2 to be achieved.

Sintering behaviour of cobalt ferrite ceramic

Pure cobalt ferrite ceramic powder was prepared using standard solid-state ceramic processing. Uniaxially pressed pure cobalt ferrite discs, sintered under isothermal ramp rate and single dwell time conditions, yielded a maximum theoretical density (%D th) of <90%. Discs made from finer particle size powder yielded a %D th of 91.5%. Based on dilatometry analysis, a sintering profile comprising non-isothermal sintering, and two-step sintering was devised, yielding discs with %D th of 96%. Cylindrical rods of pure cobalt ferrite were cold iso-statically pressed and sintered according to the revised sintering profile. Pycnometry analysis was used to quantify the percentages of open and closed pores in the rods after sintering.

Influence of processing and conduction materials on properties of co-fired resistors in LTCC structures

The motivation of this study is the need for fundamental understanding of the effects of processing conditions on the electrical properties of low-temperature co-fired ceramic (LTCC) tapes, those screen printed with commercial thick-film pastes of electronic components for increased reliability. The method of the study is realized by analyzing the physical and chemical effects of mono/multilayer firing and firing temperatures on the temperature coefficient of resistance (TCR) and sheet resistance (SR) values of the positive temperature coefficient (PTC) resistors screen-printed on LTCC tapes. The results are discussed with respect to the information obtained by the scanning electron microscopy (SEM), electro dispersive X-ray analysis (EDXS), X-ray and dilatometry analysis. It is shown that the content of pastes combined with varying processing conditions result in deviation from expected TCR and SR values due to the chemical and/or mechanical reactions.

Kinetics of transformation during supersaturation and aging of the Al-4.7mass%Cu alloy: Grain size, dilatometric, and differential thermal analysis studies

The processes taking place during supersaturation of the Al-4.7mass%Cu alloy have been studied by the methods of quantitative metallography and dilatometry. The grain growth activation energy was about 95 kJ/mol, and the exponent of time, n, was close to 0.4. Dissolution of precipitates caused two-stage shrinkage of the sample, which had activation energies of 90 kJ/mol (first stage, n=0.8) and 63 kJ/mol (second stage, n=0.4). The kinetics of the phase transformation during aging of the Al-4.7mass%Cu alloy has been studied by the dilatometry and differential thermal analysis The activation energy of the precipitation processes within the range of 50–320 °C varied between 50 and 100 kJ/mol and confirmed the results obtained previously. For the precipitation processes within the range of 320–462 °C, the activation energy varied from 226 to 300 kJ/mol. The results obtained were compared with literature data with good agreement.

Abnormal austenite–ferrite transformation behaviour of pure iron

The isochronal and isothermal austenite (γ) → ferrite (α) transformation of pure iron was measured by high-resolution dilatometry and differential thermal analysis. Both abnormal and normal transformation kinetics were recognized for the first time in pure iron according to the variation in the ferrite formation rate. The occurrence of the type of γ →α transformation strongly depends on the grain size; the transformation type changes from abnormal to normal with decreasing grain size. The abnormal transformation process involves the occurrence of additional peaks in the transformation rate for the first stage of the transformation. A phase transformation model, involving repeated nucleation (autocatalytic nucleation), interface-controlled continuous growth and incorporating correction for impingement, has been employed successfully to describe the observed kinetics of the abnormal transformation.

Crystallization of a Borosilicate Glass during Sintering Studied by Dilatometry and XRD Analysis

Crystallization of a Borosilicate Glass during Sintering Studied by Dilatometry and XRD Analysis

Balancing metallurgy and production of high strength steels

The ever increasing demands for strip with high strength and strain values and tolerances stretch the capabilities of production sites to their limits, because the high strength at room temperature has to be combined with limited loads imposed on the mill during hot rolling. The ultralow carbon bainitic steels developed to meet customers' demands have chemical compositions that extensively retard static recrystallisation. Therefore a double hit compression technique was used to quantify the static softening behaviour. High speed plane strain compression (PSC) experiments were performed to simulate actual multistand rolling schedules at semi-industrial speeds in combination with a controlled coiling simulation. The sample size allows determination of mechanical properties, microstructure, or crystallographic texture. The force–displacement curves permit more accurate tuning of the rolling models. Hence, control of thickness at the head end of the strip during hot rolling can be improved. The transformation behaviour was measured using dilatometry and thermal analysis. In combination with the mechanical properties obtained from the PSC samples, these data allowed conclusions to be drawn regarding optimum cooling rate and coiling temperature. This subsequently allowed high productivity industrial production of high strength steels having good mechanical properties, while reducing loads in the mill to acceptable levels. The work has demonstrated that the combination of metallurgical models and experiment is a powerful tool in rapid implementation of product developments.

On the glass transition domain in some M-SiAlON (M = Y or Ln) oxynitride glasses

The behaviour in the glass transition domain of some oxynitride glasses has been studied by thermoanalytical methods (dilatometry and differential thermal analysis) and mechanical techniques (creep and ultrasonic measurements of Young's modulus). The thermoanalytical data are in good agreement with the glass transition domain defined from viscosity data. The sharp decrease of Young's modulus, that starts at the temperature of the strain point, is compared to results obtained from mechanical spectroscopy by other authors. The difference in the apparent activation energies for viscous flow above and below the temperature of the strain point is used to separate the contribution of the thermal and structural components. The high temperature apparent activation energy of viscosity is in fair agreement with that of the α-relaxation peak described by the formalism of hierarchically correlated molecular mobility.