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PAMRIC: Properties of Alloys and Moulds Relevant to Investment Casting.

Chapman, L A; Morrell, R; Quested, P N; Brooks, R F; Chen, L-H*; Ford, D* (2008) PAMRIC: Properties of Alloys and Moulds Relevant to Investment Casting. NPL Report. MAT 9

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PAMRIC was a collaborative project established between NPL and industry in the field of metal casting. The objective of this project was to measure the thermophysical properties (enthalpy; heat capacity; density and thermal diffusivity) of four metal alloys and eight ceramic mould systems relevant to the investment casting industry.

The alloys chosen by the partners were the nickel alloys IN738LC; CM186LC; CMSX10 and Rene 80. The following physical properties for both the solid and liquid states of these alloys were measured between 700°C and 1500 oC.

(i) Heat capacity, enthalpy, enthalpy of fusion, fraction solid.
(ii) Thermal diffusivity and derived thermal conductivity.
(iii) Density, thermal expansion coefficient.
(iv) Solidus and liquidus temperatures.

The heat capacity measurements revealed that there were two major transitions (i) the g/g ' transformation which occurred between ca 1000-1100 oC and 1200-1300 oC and (ii) the fusion process.

The industrial partners supplied eight proprietary ceramic moulds, and for four of them fairly detailed descriptions were given of their construction, whereas little detail was given about the other four. The shrinkage on firing was measured by a simple test on the dimensions and the following other properties were measured:

(i) Heat capacity and enthalpy,
(ii) Thermal diffusivity and derived thermal conductivity.
(iii) Density, thermal expansion coefficient.
The results for the moulds carry a higher uncertainty of measurement for thermal diffusivity and heat capacity compared with the alloy results. This is attributed to the greater structural inhomogenity of the moulds. For the thermal diffusivities experimental difficulties in measuring the very small values were experienced, whereas thermal contact was perceived as a problem for the heat capacity measurements.

It is concluded that for the moulds it is probably sufficient to estimate the heat capacity from the weighted values of the main constituents of the mould rather than direct measurement. For the density (thermal expansion) the results at high temperatures are particularly affected by the time at temperature and the industrial processing conditions need to be assessed when estimating the change in dimensions of the mould. It is postulated that creep will also play some part in the change in dimensions.

Sensitivity analysis for changes in the values of the shell conductivity and heat capacity; effect of dimensional changes and interfacial conductivity for the solidification of a model casting with varying dimensions (Small; medium and large.) were performed by the industrial partners. For all parts the total solidification time was strongly effected by the thermal conductivity of the mould; changes in the heat capacity did effect initial solidification time whereas the interfacial conductivity generally had a small effect although a greater effect for thick sections.

One of the industrial partners modelled the differential scanning calorimeter (DSC) and investigated the effects of poor thermal contact between specimen and sample.

Item Type: Report/Guide (NPL Report)
NPL Report No.: MAT 9
Keywords: High-temperature alloys, ceramic casting moulds, thermal expansion, thermal diffusivity, specific heat, enthaply, modelling
Subjects: Advanced Materials
Advanced Materials > Metals and Alloys
Last Modified: 02 Feb 2018 13:15
URI: http://eprintspublications.npl.co.uk/id/eprint/4055

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