Institute of Metals Division - Influence of Tin and Aluminum on the Transition Behavior of Oxygenated Titanium

Definite transition behavior was found in unalloyed titanium at 0.13 pct 0 equivalent. The addition of 0.5 Sn, 1.0 Al, 0.5 Al, and 1.0 Sn lowers the tvansition temperature of titanium at oxygen equivalents exceeding 0.22, 0.29, 0.40, and 0.51, respectively. Metallographic evidence indicates that progressive amounts of oxygen restrict deformation at low temperatures resulting eventually in brittle fracture. The presence of tin or aluminum is thought to alter the atomic distribution of oxygen within the titanium lattice in such a manner as to facilitate some degree of slip and twinning. 1 ITANIUM-like iron and zinc experiences a transition from ductile to brittle fracture with decreasing temperature. The presence of sufficient quantities of the interstitial elements, carbon, oxygen, and nitrogen in solid solution, has been shown to progressively lower the room-temperature impact resistance of titanium with increasing interstitial content.1"1 Ogden,et al,2 reported finding no transition from ductile to brittle fracture with decreasing temperature in iodide titanium. However, a definite transition was found to occur at 0.36 pct 0 equivalent in an alloy containing 0.47 pct carbon in solid solution. The oxygen equivalent in this case was obtained by assuming the effects of carbon, oxygen, and nitrogen in combination on the impact properties of titanium to be additive on the same basis as their separate effects on tensile strength, namely: Oe = 2/3 (pct C) + pet 0 + 2 (pet N) They concluded that the tendency toward transition behavior is dependent on the total interstitial content in solid solution and not on any one particular interstitial element. Rennhack,4 however, recently found transition behavior in iodide titanium at an oxygen equivalent of 0.17 pct. Ogden, etal3, reported that the strengthening effects of carbon, oxygen, and nitrogen in titanium decrease with the addition of tin. They showed that tin additions increase the tolerance of titanium for the interstitials, that is, 10 pct Sn permitted individual additions of up to 0.4 wt pct of the interstitial elements without any significant loss in ductility. Aluminum tends to decrease ductility and impact strength of titanium for a given interstitial ~ontent.3 Van Thyne and Kessler5 found that the solid solubility of carbon in titanium doubled in the presence of 10 pct Al. The precise effects of tin and aluminum in the nrespncp of rorvfen nn the impact properties of titanium had previously not been determined. The high oxygen tolerance of titanium containing tin may provide a suitable means for improving the impact properties of titanium containing the interstitial elements, particularly oxygen. Unlike tin, however, aluminum has a high affinity for oxygen and will reduce rutile titanium dioxide (TiO2)by a thermit-type reaction.6 Thus, the atomic distribution of oxygen in titanium might be different in the presence of aluminum. The present work was undertaken to: 1) Determine the effect of oxygen on the transition behavior of unalloyed iodide titanium. 2) Determine the effect of small amounts of tin and aluminum on the transition behavior of iodide titanium in the presence of oxygen and other interstitial~. EXPERIMENTAL Three different lots of iodide titanium were employed to prepare the alloys studied in the present work. Their chemical composition is presented in Table I. The compositions of the tin and aluminum used for alloying are shown in Table 11. Oxygen additions were made using calcined rutile titanium dioxide (TiO2)of 99.7 pct purity. Alloy Preparation—Four titanium-base alloys containing separate additions of 0.5 and 1.0 pct each