High Pressure X-Ray Study of Anomalous Bulk Modulus of an Fe70Ni30 Invar Alloy
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Pressure dependence of the lattice constant is measured for the pressure-stabilized fcc phase of an Fe 70 Ni 30 Invar alloy by high pressure X-ray diffraction method at 77.4 K. The bulk modulus B in the ferromagnetic phase is obtained to be (14 ±1) ×10 2 kbar. A discontinuous increase in B , Δ B , is found to be Δ B ≈700 kbar near 64 kbar. The magnitude Δ B at 77.4 K is the same as that observed at the ferromagnetic to paramagnetic phase transition at room temperature around 15 kbar.Keywords:
Invar
Lattice constant
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Nanoscaled, compositionally modulated multilayer alloys of NiFe in the Invar range and Cu were electroplated into an array of cylindrical microrecesses in polymethylmethacrylate in diameter, tall, with a center-to-center spacing of . Deposition conditions were determined using a rotating Hull cell and linear sweep voltammetry. The presence of the nanoscale multilayers was confirmed by transmission electron microscopy and the thermal expansion of the multilayer microposts was measured over the range from . As deposited, the multilayer alloy exhibited a negative coefficient of thermal expansion (CTE); for a thick Cu layer the CTE was up to and more negative for higher temperatures. To the best of the authors' knowledge this is the first observation of a room temperature, negative CTE in multilayered-Invar alloys. After thermal cycling, the alloy had a small positive CTE of up to , comparable to that of bulk Invar (, and no increase of the CTE was observed for temperatures up to .
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Negative Thermal Expansion
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Thermal expansion characteristics of Fe39Co51Cr10 based stainless invar alloys were investigated with the aim of developing a novel structural material used at cryogenic temperature for infrared instruments mounted on astronomical telescopes. Ni-added stainless invar type alloys Fe39Co49Cr10Ni2 were found to exhibit anomalous thermal expansion behavior in the low temperature range between 100 K and room temperature. According to the measured thermal expansion curves, these alloys expanded with increasing temperature from approximately 100 K to 200 K and contracted from 200 K to 300 K. The coefficients of thermal expansion in each temperature range were estimated to be approximately 0.93 x 10-6 /K and −0.71 x 10-6 /K, respectively. As the results of thermal expansion measurements of Cr based alloys, similar negative thermal expansion behavior was observed in the same temperature range between 200 K and 300 K. These findings suggest that the Cr element plays a key role in the negative thermal expansion in the Fe39Co49Cr10Ni2 alloys. We concluded that the dimensional change between 100 K and room temperature could be precisely controlled in the extremely low thermal expansion range by controlling the negative thermal expansion. The coefficient of thermal expansion between 100 K and 300 K was achieved to be approximately 0.13 x 10-6 /K in the Fe38.4Co49.7Cr10.1Ni1.8 alloys developed in this study. As this value was close to that of the fused silica used for infrared instruments, the developed alloys can be a powerful tool for high precision observation in astronomical telescopes.
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Atmospheric temperature range
Negative Thermal Expansion
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We summarize a large number of ultraprecise thermal expansion measurements made on seven different low expansivity materials. Expansion coefficients in the -150-300 degrees C temperature range are shown for Owens-Illinois Cer-Vit C-101, Corning ULE 7971 (titanium silicate) and fused silica 7940, Heraeus-Schott Zerodur low-expansion material and Homosil fused silica, Universal Cyclops Invar LR-35, and Simonds Saw and Steel Super Invar.
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Michelson interferometer was designed for measuring the thermal expansion coefficients of the ternary Fe-NiCo alloys and the binary Fe-Ni alloys with different chemical compositions at the temperature range from 25 ℃ to 65 ℃.The experiment results show that the thermal expansion coefficients of the ternary Fe64Ni36-xCoxalloys are strongly dependence on its chemical composition; the thermal expansion coefficient of the Fe64Ni31Co5 alloy reaches a minimum value of 0. 79 × 10- 6/℃,deviation from the composition of the Fe64Ni31Co5 alloy,the thermal expansion coefficients increase. The thermal expansion coefficients of the binary Fe-Ni alloys are also strongly dependence on its chemical composition; the thermal expansion coefficient of the Fe65Ni35 alloy reaches a minimum value of 1. 58 × 10- 6/℃,deviation from the composition of the Fe65Ni35 alloy,the thermal expansion coefficients increase. The thermal expansion coefficient of the Fe64Ni31Co5super-invar alloy is lower than that of the Fe65Ni35 invar alloy. The variation of the thermal expansion coefficient of the binary Fe-Ni alloy with Ni content is relatively large,while the variation of the thermal expansion coefficient of the ternary Fe64Ni36- xCoxalloy with Co content is relatively small.
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Invar Fe-Ni alloy is a prominent Ni steel alloy with a low coefficient of thermal expansion around room temperature. We investigate the correlation between magnetic properties and thermal expansion in cold-drawn Fe-36Ni wires with different heat treatment conditions, where the annealing parameters with furnace cooling (cooling from the annealing temperature of 300, 400, 500, 600, 700, 800, 900, and 1000 °C) are used. The variation trend of magnetic properties is consistent with that of thermal expansion for all samples, where the maximum appears at 600 °C -treated sample and 400 °C shows the minimum. The domain size and the area of domain walls determine the total energy of the domain wall, and the total energy directly determines the size of magnetostriction, which is closely related to the coefficient of thermal expansion. Also, the differential thermal analysis (DTA) shows endothermic and exothermic reactions represent crystalline transitions, which could possibly cause the abrupt change of magnetic properties and thermal expansion coefficient of materials. The results indicate that there is a certain relation between thermal expansion and magnetic properties. Besides the fundamental significance, our work provides an Invar alloy with a low coefficient of thermal expansion for practical use.
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Thermomechanical analysis
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This work investigated the linear thermal expansion properties of a multi-material specimen fabricated with Invar M93 and A36 steel. A sequence of tests was performed to investigate the viability of additively manufactured Invar M93 for lowering the coefficient of thermal expansion (CTE) in multi-material part tooling. Invar beads were additively manufactured on a steel base plate using a fiber laser system, and samples were taken from the steel, Invar, and the interface between the two materials. The CTE of the samples was measured between 40 °C and 150 °C using a thermomechanical analyzer, and the elemental composition was studied with energy dispersive X-ray spectroscopy. The CTE of samples taken from the steel and the interface remained comparable to that of A36 steel; however, deviations between the thermal expansion values were prevalent due to element diffusion in and around the heat-affected zone. The CTEs measured from the Invar bead were lower than those from the other sections with the largest and smallest thermal expansion values being 10.40 μm/m-K and 2.09 μm/m-K. In each of the sections, the largest CTE was measured from samples taken from the end of the weld beads. An additional test was performed to measure the aggregate expansion of multi-material tools. Invar beads were welded on an A36 steel plate. The invar was machined, and the sample was heated in an oven from 40 °C and 160 °C. Strain gauges were placed on the surface of the part and were used to analyze how the combined thermal expansions of the invar and steel would affect the thermal expansion on the surface of a tool. There were small deviations between the expansion values measured by gauges placed in different orientations, and the elongation of the sample was greatest along the dimension containing a larger percentage of steel. On average, the expansion of the machined Invar surface was 42% less than the expansion of the steel surface. The results of this work demonstrate that additively manufactured Invar can be utilized to decrease the CTE for multi-material part tooling.
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Thermomechanical analysis
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Invar
Atmospheric temperature range
Negative Thermal Expansion
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The coefficient of thermal expansion (CTE) of a hot pressed Ta16W18O94 which was produced from Ta2O5 and WO3 powders was found to be −1.52×10−6 K−1 in the temperature range 180–330 K. Using the Ta16W18O94 and Super Invar powders, 50:50 volume percent metal-ceramic composites were made by the powder metallurgy techniques. When the mixture of constituent powders was hot pressed at 1123 K for 10 minutes, a CTE of 1.1 × 10−6 K−1 was obtained in the temperature range 140–420 K.
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Powder Metallurgy
Atmospheric temperature range
Volume expansion
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