Institute of Metals Division - Internal Friction in Zirconium

Internal friction characteristics and temperature dependence of the torsion modulus for iodide zirconium containing 2.4 pct Hf were investigated, using a low frequency pendulum technique. The internal friction curve consists of a background which increases as the temperature increases, a maximum at 860°C apparently a background due to the al-lotropic transformation, a maximum due to grain boundary relaxation with an associated heat of activation of 58,000 cal per mol, and an anomaly below 350°C which may be associated with a precipitation perphenomenon, Oxygen in below small amounts reduces the grain boundary maximum substantially. The variation of the torsion modulus at 20°C was found to be 3450 Kg per mm2 for the zirconium used in the present work. IT is well known that small amounts of certain solutes materially affect the ductility of zirconium. Lely and Hamburger,&apos; as early as 1914, found that high purity zirconium exhibited a remarkable ductility, while Fast&apos; has shown that oxygen and nitrogen can cause substantia1 embrittlement. Treco" has recently demonstrated that the ductility decreases sharply with the oxygen content, and that 2 atomic pct O2 embrittles zirconium to such an extent that cold working is impossible. The marked decrease in ductility is difficult to understand in view of the fact that Domagala and McPherson4 report the solid solubility of oxygen in zirconium to be 29 atomic pct at 500 °C. Another metal which behaves much the same as zirconium in this respect is titanium. Pratt et al." investigated the internal friction characteristics of titanium and the effect of oxygen on the internal friction values. It is evident that internal friction measurements are of value for studying grain boundary segregation, as shown by Pratt et al. for oxygen in titanium, by Pearson for oxygen in copper, and by Maringer and Schwope for oxygen in molybdenum. With this in view, the internal friction characteristics of zirconium and the qualitative effect of oxygen on the grain boundary relaxation phenomenon were investigated. Materials and Experimental Procedure The zirconium used in the present work was supplied by the Foote Mineral Co. in the form of wire 0.05 in. diam. The analysis supplied by the manufacturer indicates the amount of hafnium as 2.4 pct, less than 0.01 pct O less than 0.01 pct N,, less than 0.02 pct H,, and less than 0.001 pct C. Additional spectro-graphic analysis indicates the other main impurities as follows: 0.01 pct Fe, 0.05 pct Si, 0.008 pct Cu, <0.005 pct W, <0.001 pct Al, <0.05 pct Mg, <0.001 pct Ni, <0.02 pct Ca, and <0.01 pct Ti. Microscopic examination of the material in the as received condition revealed very fine grains with numerous twins. Specimens were annealed either in situ in the internal friction apparatus or in evacuated silica tubes in an auxiliary furnace. When the specimens were annealed in the auxiliary furnace, they were wrapped in identical zirconium wire to prevent contamination by the container. Metallographic sections were taken in all cases. Some were taken from the specimens used for internal friction measurements after completion of the experiments, while others were taken from control specimens at intermediate stages of the experiments. lnternal friction values were obtained by measuring the free decay of a low frequency torsion pendulum (1 cycle per sec), the suspension of which was