Coupling of Computational Thermodynamics with Kinetic Models for Predictive Simulations of Materials Properties

We present successful examples of CALPHAD thermodynamics-based precipitation simulations for three important alloy groups: Single-crystal Ni-base superalloy, austenitic stainless steel and hardenable Al-alloy. Underlying physical models for special features, such as, energies of diffuse interfaces between coherent precipitates and matrix, precipitation of incoherent particles at grain boundaries, evolution of excess vacancies during quenching and continuous aging and their role for metastable precipitate nucleation, are discussed.

A Study of Effects of Precipitation Hardening of Low-Alloy Copper-Nickel Spheroidal Cast Iron

One type of spheroidal cast iron, with additions of 0.51% Cu and 0.72% Ni, was subjected to precipitation hardening. Assuming that the greatest increase in hardness after the shortest time of ageing is facilitated by chemical homogenisation and fragmentation of cast iron grain matrix, precipitation hardening after pre-normalisation was executed. Hardness (HB), microhardness (HV), qualitative and quantitative metalographic (LM, SEM) and X-ray structural (XRD) tests were performed. The acquired result of 13.2% increase in hardness after ca. 5-hour ageing of pre-normalised cast iron confirmed the assumption.

Determination of trace elements in the Pb–Bi-eutectic system by inductively coupled plasma-quadrupole mass spectrometry after sequential removal of the matrix by precipitation

Matrix precipitation for the sensitive determination of impurities in the Pb–Bi eutectic system by ICP-MS.

Significance of Low Copper Content on Grain Boundary Nanostructure and Intergranular Corrosion of AlMgSi(Cu) Model Alloys

Intergranular corrosion (IGC) of model alloys in the 6000-series, with and without 0.2 wt% Cu, was studied using an accelerated corrosion test (BS ISO 11846 B), FE-SEM and FE-TEM. Low Cu alloys (0.02wt%) did not exhibit IGC even though they contained excess Si. The high-Cu, naturally aged material (T4) was susceptible to severe superficial etching. In the underaged state (below peak strength), the Cu-containing material was highly susceptible to IGC. Materials aged to peak strength (T6) or overaged were only slightly susceptible to IGC, with localized, shallow attacks. FE-TEM investigation of the underaged material revealed scattered, small AlMgSiCu-type precipitates, as well as a Cu-enriched film along the grain boundaries. The overaged material showed more extensive, coarse grain boundary precipitation. However, the Cu-enriched film was still present at localized sites. The reduced susceptibility to IGC upon artificial ageing was attributed to breaking of the continuity of the grain boundary film. The possible role of matrix precipitation is also discussed.