A. Baldan

Bio: A. Baldan is an academic researcher from Council of Scientific and Industrial Research. The author has contributed to research in topics: Superalloy & Creep. The author has an hindex of 2, co-authored 2 publications receiving 13 citations.

Effects of carbides and cavitation on the Monkman-Grant ductility of a nickel-base superalloy

Abstract: The \"constant\" CM in Equation 2 is sometimes called the Monkman-Grant \"ductility\", which is of the nature of a strain (by necessity always smaller than the actual creep rupture strain OR). Under the condition of the constrained cavity growth, distribution of cavities would be expected to be quite inhomogeneous with only the transverse grain boundaries being heavily cavitated. In these circumstances cavity growth can be controlled by creep flow of the surrounding matrix, which may explain the success of the Monkman-Grant relationship. The object of this study was to determine the effect of the carbide precipitates and cavitation on the Monkman-Grant \"ductility\" for conventionally cast IN-100 superalloy. The bulk composition of this alloy (by wt%) is: 10.0 Cr, 15.0 Co, 4.7 Ti, 5.5 A1, 3.0 Mo, 0.18 C, 0.06 Zr, 0.014 B, 1.0 V and balance Ni. The following conditions were used to produce the different initial carbide dispersions along the grain boundaries: as-cast structure at different cooling rates; heat treatment A (1107 °C for 4 h, furnacecooling, plus 871 °C for 12 h, furnace-cooling) heat treatment B (1220 °C for 1 h, furnace-cooling, plus 1100 °C for 1 h, furnace-cooling). The creep testing was carried out up to failure at 1173 K by uniaxial constant-load testings, and the initial stress was 276 MPa. Creep specimens with 4 .0mm gauge diameter were used. The creep elongation was recorded continuously using differential transformers. Assessments of the amount of intergranular creep cavitation damage after fracture and metallographic measurements of initial carbides were made using scanning electron microscopy and a Cambridge Q 520 instrument. Using the different casting and heat-treatment

On the thin-section size dependent creep strength of a single crystal nickel-base superalloy

Abstract: The combined effects of thin-section size, D, and microcracks on the creep behaviour of the single crystal MAR-M002 were investigated at the creep conditions of 300 MPa and 900 °C. It was observed that the creep rupture life, tR is controlled by the mean microcrack size to thin-section size, (dc/D), (or the total number, (Nm), of the mean-sized microcrack particles across the diameter, assuming D/dc=Nm); reducing Nm continuously improves tR. The creep rupture strain (or ductility), eR, can be improved sharply by increasing the total number, NT, of microcrack particles across the cross-section, NT ∝ D2NA, where NA is the number of microcrack particles (cavity density) per cross-section. The behaviour of the creep rupture ductility was interpreted in terms of the weakest link, or “largest-flaw” concept; the observation of the higher proportion of the less likely dangerous (smaller in size) microcracks with increasing NT was the underlining reason for the improvement in ductility.

Effects of HIP Temperature on the Microstructural Evolution and Property Restoration of a Ni-Based Superalloy

Abstract: The effects of hot isostatic pressing (HIP) temperature on the evolution of microstructural characteristics around the creep cavities were investigated using five different soaking temperatures during HIP. The restoration of microstructural and material properties under these HIP schedules followed by the same rejuvenation heat treatment (RHT) procedure was then evaluated. The results showed that HIP temperature played a dominant role in the cavity healing process, determining the evolution features of cavities and hence the extending ratio of rupture life. With gradually increasing the adopted HIP temperature, the cavity healing behaviors were revealed. Concentrically oriented N-type γ′ rafting structure in the vicinity of the healing cavity was observed at an appropriate soaking temperature. The driving force for the cavity healing was considered to be the chemical potential gradient induced by the stress gradient field around the cavity. The appropriate HIP schedule followed by RHT process significantly improved the rupture life of damaged alloy, and the extending ratio varied with the adopted HIP temperature.

Creep Lifing Models and Techniques

Abstract: The deformation of structural alloys presents problems for power plants and aerospace applications due to the demand for elevated temperatures for higher efficiencies and reductions in greenhouse gas emissions. The materials used in such applications experience harsh environments which may lead to deformation and failure of critical components. To avoid such catastrophic failures and also increase efficiency, future designs must utilise novel/improved alloy systemswith enhanced temperature capability. In recognising this issue, a detailed understanding of creep is essential for the success of these designs by ensuring components that do not experience excessive deformation which may ultimately lead to failure. To achieve this, a variety of parametric methods have been developed to quantify creep and creep fracture in high temperature applications. This study reviews a number of well-known traditionally employed creep lifing methods with some more recent approaches also included. The first section of this paper focuses on predicting the long-term creep-rupture properties which is an area of interest for the power generation sector. The second section looks at pre-defined strains and the re-production of full creep curves based on available data which is pertinent to the aerospace industry where components are replaced before failure.