Reproducibility of small-strain creep tests of Ti 6242Si

Titanium 6242Si was creep tested at 510 deg C and 241 MPa to plastic strains of approx0.002. These conditions are common in commercial specifications for acceptance of this alloy. Nineteen specimens were extracted from four identically thermally and mechanically processed coupons from the same ingot and creep tested. The results indicate relatively poor reproducibility despite essentially identical sample preparation and specimen testing procedures. The causes of the scatter are unclear. The average creep strain of the 19 specimens after 35 h was 0.067%, and the standard deviation was 0.0367%. Significant scatter is also evident among the average properties of the four coupons. The results suggest that impurity levels and processing procedures may require adjustments to ensure relatively low expected or "average" creep strain levels (half the allowable) in some common acceptance specifications to ensure a high probability of acceptance.