Donald McLean had an important and enduring influence on the science and engineering of materials for structural applications
Donald McLean has been an important and enduring influence on the science and engineering of materials for structural applications, including deformation and failure at elevated temperatures. He provided a formal basis for two important fields of study: grain boundaries, and creep deformation and fracture due to cavitation. In addition, he has significantly influenced other areas of physical metallurgy and, of particular importance, he pioneered the application of quantitative analysis of micromechanisms to engineering design and life assessment.
Donald McLean joined NPL in 1947 and, during service spanning nearly 30 years, his influence on metallurgical research was considerable. His early work on the creep of metals at elevated temperatures demonstrated the importance of grain boundary sliding. This required difficult measurements performed by elegant optical microscopy, and provided the basis for much subsequent thinking on the mechanisms involved. His interest in grain boundaries continued throughout his career, leading to the publication of his book Grain Boundaries in Metals.
Later, he became concerned with the quantitative aspects of fracture during creep deformation that is caused by the nucleation and growth of cavities at grain boundaries, and from these developed methodology that he called 'predictive metallurgy'. This enabled the prediction of materials behaviour using rules governing the underlying physical processes leading to reduced dependence on empiricism.
A second book, The Mechanical Properties of Metals, reflected a wide interest in defects in solids. Dr McLean was one of the first to realise the importance of dislocations during the deformation of metals, and was much involved in applying high voltage electron microscopy to examine their behaviour. Amongst many results, he was able to establish experimentally the relationship between dislocation density and flow stress.