The effects of thermal exposure on the high temperature behaviour of a Laser Powder Bed Fused nickel based superalloy C263

Additive manufacturing (AM) processes are currently being investigated to determine their suitability for wider adoption in the aero engine industry where material consistency and structural integrity are essential. A key driver is the ability of AM to produce near net-shape components and complex geometries, reducing material wastage and traditional processing stages. However, one major limitation remains in the anisotropic structures due to the complex thermal history of the process. Previous studies have employed heat treatment schedules attempting to alleviate such behaviour, although little research is currently available that explores microstructural evolution of AM alloys at in-service temperature conditions. In this research, the effects of thermal exposure on microstructure and mechanical behaviour of Laser Powder Bed Fused (LPBF) C263 is evaluated and assessed against a Cast equivalent. Results show that when exposing Cast and LPBF C263 samples to service temperatures for an extended period of time, the materials experience microstructural and chemical alterations directly controlling the mechanical response. The thermal exposure programme has demonstrated that with the precipitation of carbide phases in the exposed LPBF variant, grain boundary morphologies are highly comparable to the wrought equivalent of the same alloy

Alloying effect on solidification behaviour and grain refinement in Ti45Al2Nb2Ta0.8B and Ti45Al2Nb2Hf0.8B

The solidification process of Ti45Al2Nb2Ta0.8B (B4522Ta) and Ti45Al2Nb2Hf0.8B (B4522Hf) Bridgman samples were studied through directional solidification. Boron addition at 0.8 at. % was found to have changed the orientation relationship of peritectic α with β dendrites. The peritectic alpha is randomly oriented in both B4522Ta and B4522Hf, it was likely to be inoculated by boride precipitates at the β/liquid interfaces during peritectic transformation. The alloying effect of Ta and Hf on the peritectic reaction was similar. Borides precipitated earlier in Ta-containing alloy than that in Hf-containing alloy during solidification

Small Punch Creep

A thorough characterisation of the creep properties of any modern alloy designed for a structural application can be an expensive and timely process. As such, significant effort is now being placed in identifying suitable alternative characterisation techniques. The small punch creep (SPC) test is now widely regarded as an effective tool for ranking and establishing the creep properties of a number of critical structural materials from numerous industrial sectors. Over recent years, the SPC test has become an attractive miniaturised mechanical test method ideally suited for situations where only a limited quantity of material is available for qualification testing. Typically, the method requires only a modest amount of material and can provide key mechanical property information for highly localised regions of critical components. As such, SP creep testing offers a feasible option of determining the creep properties of novel alloy variants still at the experimental stage and the residual life of service-exposed material

Derivation of material properties using small punch and shear punch test methods

The Small Punch (SP) and Shear Punch (ShP) tests are well established mechanical test approaches that have found application in several industrial sectors for material ranking and mechanical property estimation, particularly where more conventional approaches are inhibited. Despite the advantages that the two test methodologies have to offer, the main drawback is the complex understanding of the mechanical data generated from the experiments and how it can be correlated to more recognised properties. Typically, the most desired properties relate to the uniaxial properties of yield stress, ultimate tensile strength and ductility, but to date, there is no single robust and overarching approach for correlating such properties for a wide array of metallic materials that exhibit varying levels of ductility. This paper will for the first time directly compare properties obtained from a series of uniaxial tensile, SP and ShP tests across several metallic materials, and look to establish and correlate equivalent properties across the different test types. The materials investigated range from commercially pure entities to more advanced alloy systems. The generated results, empirical relationships and numerical simulations will inform which materials can be correlated across the different test regimes, and identify why the relationship in certain materials breaks down

The contribution of small punch testing towards the development of materials for aero-engine applications

This paper, invited for presentation at the 33rd Meeting of the Spanish Group on Fracture and Structural Integrity, March 2016 in San Sebastian, Spain, reviews the recent work carried out in the authors’ laboratory, addressing the elucidation of tensile and creep characteristics of materials for aero engine components. Two specific applications of the Small Punch (SP) test assessment technology were identified, the first of these takes on board the unique potential of the SP test for testing small quantities of materials which are either in development or through their directional structure cannot easily be produced in quantities which would allow conventional mechanical testing. This goal also required the development and procurement of new SP test facilities capable of operation up to 1150 °C. The examples given in this paper are TiAl intermetallic alloys and nickel based single crystals, all studied utilising the Code of Practice for SP Creep Testing. The second application illustrates the use of SP testing to assess both the tensile and creep properties of additive layer manufactured (ALM) alloys such as IN718 and Ti-6Al-4V using the Code of Practice for SP Tensile and Fracture Testing. Due to the unavailability of sufficient material to facilitate conventional testing for comparison of materials property data, SP testing is unable to provide absolute data for all of these applications, nevertheless the ranking capabilities of SP testing are demonstrably proven

Development of a Novel Methodology to Study Fatigue Properties using the Small Punch Test

Small scale mechanical test methods are now widely recognised as an established and quantifiable means of obtaining useful mechanical property information from limited material quantities. Much research has been gathered employing such approaches, but to date these methods have largely been restricted to characterising the creep, tensile and fracture characteristics of numerous materials and alloys through the small punch (SP) test. Clearly, a key element that is missing from this list of fundamental mechanical properties is understanding the cyclic response of the material, a significant form of damage that accounts for a large proportion of in-service failures in critical structural components. Therefore, in order to profit from the numerous benefits that SP testing has to offer, including a small sample size and hence reduced cost, a small scale fatigue testing methodology is now required to provide a holistic mechanical property evaluation. Such an innovative approach would provide real potential benefit to the engineering mechanical characterisation community. This paper will discuss the development and implementation of this highly bespoke SP fatigue testing methodology that can accommodate alternative loading ratios and frequencies to mimic conventional fatigue data. A number of novel experiments have been performed on the titanium alloy Ti-6Al-4V with accompanying analysis and fractography detailed. Numerical correlations to uniaxial fatigue data is also presented through the use of Finite Element Analysis

Elevated Temperature Creep Deformation of a Single Crystal Superalloy through the Small Punch Creep Method

Small punch testing is now a widely recognised approach for obtaining useful mechanical property information of critical structural components, particularly in the nuclear industry. However, to date the utilisation of this method has been limited to isotropic materials such as aluminium alloys and steels. This paper will look to utilise the small punch (SP) test to assess the creep response of 〈001〉-orientated CMSX-41 at temperatures above 950 °C. An orthogonal rafting regime of the γ′ structure is observed in the post-test microstructure due to the biaxial tension state typically produced in a SP test. Interpretation of the SP results to correlate with uniaxial creep data is carried out by employing the ksp approach in order to provide a platform for future material assessment

Characterising the high temperature tensile behaviour of laser powder bed fused duplex stainless steel 2205 using the small punch test

Duplex stainless steels (DSS) are a family of stainless steel alloys that benefit from the presence of two relatively equally proportioned phases, ferrite and austenite. The alloys are designed to have an enhanced resistance to corrosion and superior strength properties in comparison to more common stainless steel alloys such as 316 L. Design engineers are now exploring the introduction of additively manufactured (AM) DSS into industrial components, to benefit from these enhanced capabilities provided by the alloy and the greater flexibility in design offered by AM. This research focuses on the mechanical and microstructural characterisation of DSS 2205, manufactured by the AM process laser powder bed fusion (LPBF). Results have been generated through both uniaxial tensile testing and small punch (SP) testing on as built and heat-treated conditions, across a range of temperatures up to 750 °C. Microstructural assessments have been conducted using advanced microscopy to determine relevant phase distributions and texture morphologies present in the materials, to understand how this influences mechanical performance

Structural Integrity of an Electron Beam Melted Titanium Alloy

Advanced manufacturing encompasses the wide range of processes that consist of “3D printing” of metallic materials. One such method is Electron Beam Melting (EBM), a modern build technology that offers significant potential for lean manufacture and a capability to produce fully dense near-net shaped components. However, the manufacture of intricate geometries will result in variable thermal cycles and thus a transient microstructure throughout, leading to a highly textured structure. As such, successful implementation of these technologies requires a comprehensive assessment of the relationships of the key process variables, geometries, resultant microstructures and mechanical properties. The nature of this process suggests that it is often difficult to produce representative test specimens necessary to achieve a full mechanical property characterisation. Therefore, the use of small scale test techniques may be exploited, specifically the small punch (SP) test. The SP test offers a capability for sampling miniaturised test specimens from various discrete locations in a thin-walled component, allowing a full characterisation across a complex geometry. This paper provides support in working towards development and validation strategies in order for advanced manufactured components to be safely implemented into future gas turbine applications. This has been achieved by applying the SP test to a series of Ti-6Al-4V variants that have been manufactured through a variety of processing routes including EBM and investigating the structural integrity of each material and how this controls the mechanical response