An analysis of small punch creep behaviour in the γ titanium aluminide Ti–45Al–2Mn–2Nb

Abstract

a b s t r a c tPrevious literature on gamma titanium alumindes (γ-TiAl) have found that this family of alloys offer significant potential for replacing more conventional nickel and titanium based alloy systems in future designs of gas turbine engines. Despite the inherent brittle nature of such materials, γ-TiAl typically exhibits considerable ductility at elevated temperatures and a demonstrable uniaxial creep response. Until now, the creep properties of γ-TiAl have primarily been sourced from conventional uniaxial approaches, which require significant material quantities in order to perform a full stress-temperaturelife assessment. This is not always possible for new alloys where sufficient quantities of material are unavailable. The small punch (SP) creep test represents an attractive alternative to uniaxial creep testing since the volume of material required is much less. However, much of the current literature on SP testing is limited to the application of traditionally ductile materials. This paper assesses the suitability of the SP method to characterise the creep properties of γ-TiAl alloys. Finite element modelling has been used to characterise the SP deformation and rupture behaviour.

Application of the small punch test to determine the fatigue properties of additive manufactured aerospace alloys

“…To date these methods have largely been adopted to characterise the creep [3], [4], tensile [5], [6] and fracture characteristics [7], [8] of numerous material systems [9], [10] from a range of industrial applications for sampling [11], [12]. This paper will now detail the research undertaken in realising a small-scale test methodology capable of characterising the localised fatigue properties of ALM built structures.…”

Small Punch Creep

“…Previous research [13,23] has demonstrated that the shape of the time displacement/deflection curves from SP creep tests are qualitatively similar and representative of the shape typically observed from uniaxial testing approaches. Now, over recent years, many researchers and scientists have devoted significant effort in establishing a series of correlative means capable of comparing the results obtained from SP creep testing to data gathered from more traditional creep testing methodologies.…”

“…In contrast, SP testing has also been employed to characterise the creep properties of more inherently brittle type materials, such as γTiAl [23] or Mg alloys [24]. Figure 9 presents the typical fracture morphology for a brittle small punch disc.…”

“…Nevertheless, the Chakrabarty model has its limitations in that it is only really suitable for large deformations which is not always the case with brittle materials where specimens may crack upon loading or in the early phase of the test [23], or fractures that reveal a star type pattern as illustrated earlier [18]. In addition, any strain hardening effects must be considered rather than an exponential hardening law only as is the case here [32].…”

“…• Finally, the technique has long been adopted as a means of determining equivalent or correlated uniaxial properties over a wide range of material systems including nickel based single crystal material ® CMSX-4 [21,22], γ-titanium aluminide [23], aluminium alloys [24] and stainless steel [25].…”