Yield Points in Zinc Crystals

It is shown that sharp yield points can be produced in crystals of zinc containing nitrogen The gas is introduced in a preliminary melting operation, either by bubbling it through the metal or by allowing it to be absorbed from the atmosphere, using a flux to keep the surface clean. Strain ageing treatments are needed to develop the yield point clearly, but once it is developed it returns at the same level after each successive treatment at the same temperature Ageing experiments at room temperature show that overstrained zinc crystals soften by recovery before the yield point returns; zinc differs from iron in this respect. General conditions for producing yield points in metals of common crystal structures are briefly discussed.