Heat Treatment Effects on Pristine and Cold-Worked Thin-Walled Inconel 625

Thin-walled Inconel 625 sheet metal was sectioned into tensile specimens, plastically strained, and then heat treated. Specimens were pulled to a targeted strain, unloaded, and then subjected to one of two heat treatments with the goal of restoring the full ductility and total plastic strain capability of the material. Post-heat treatment tensile testing was performed at room temperature to evaluate the heat treatment efficacy and then followed by hardness and microstructural analysis. The results showed the amount of material recovery was affected by the initial amount of plastic strain imparted to the tensile specimen before heat treatment. Although recrystallization was not observed, grains did elongate in the load direction, and the Kernel average misorientation (KAM) increased with heat treatment. Furthermore, specimens prestrained to 40% and heat treated at 980 °C successfully recovered 88% of pre-heat treatment strain capability prior to fracturing.

High-Throughput Statistical Interrogation of Mechanical Properties with Build Plate Location and Powder Reuse in AlSi10Mg

Additive manufacturing (AM) allows agile, rapid manufacturing of geometrically complex components that would otherwise be impossible through traditional manufacturing methods. With this maturing manufacturing technology comes the need to adopt testing methods that are commensurate with the speed of additive manufacturing and take advantage of its geometric flexibility. High-throughput tensile testing (HTT) is a technique that allows a large number of tensile bars to be tested in a short amount of time. In the present study, HTT is used to evaluate AM AlSi10Mg produced using powder bed fusion with a Renishaw AM250 machine. Three parameters were varied in this study: (1) powder reuse history, (2) location on the build plate, and (3) size of the tensile specimen. For all parameter combinations, at least 22 specimens were tested; in several cases, over 40 were tested. This large dataset, consisting of over 500 tensile tests, permits Weibull statistical analysis and provides sufficient fidelity to isolate subtle trends that would have likely been missed in smaller, traditional datasets. The observed trends are rationalized in terms of the role of porosity and surface crust on mechanical response.

Microstructural and Mechanical Behaviors of Friction Stir Welded Dissimilar AA6082-AA7075 Joints

In this research, microstructural events and mechanical behaviors in dissimilar friction stir welding (FSW) of aluminium (Al) alloy AA6082-AA7075 joints have been evaluated to apply aerospace, defense, and military sectors. FSW parametric effects have a more significant impact on the mechanical performances and microstructure of produced joints. FSW tool rotational speed, welding speed, and tool plunge speed were chosen to make the weld joints. The rotational tool speeds of 1600 rpm and 2300 rpm, welding speeds of 40 mm/min and 60 mm/min, and tool plunge speeds of 20 mm/min and 30 mm/min were set as the upper and lower limits. A constant axial force of 5 kN was maintained throughout the joint fabrication process. A taper pin-profiled tool was utilized to produce the butt welded joints. Mechanical properties of microhardness, tensile strength, yield strength, elongation, and bending strength of the joints were analyzed. The response of the stir zone microstructure to processing parameters was evaluated using optical microscopy (OM) and fractographic analysis of a tensile specimen shown by scanning electron microscope (SEM). The weld joints produced at 2300 rpm, tool traveling rate of 40 mm/min, and tool plunge speed of 30 mm/min showed the greatest tensile strength of the 191 MPa hardness of 145 Hv at the weld center and also the maximum bending strength of 114.23 N/mm2 was achieved. The lowest bending strength of 25.38 N/mm2 was obtained at 1600 rpm with 60 mm/min due to inappropriate mixing of the base metals and poor joint quality. Furthermore, this study revealed that a higher tool plunge speed facilitates the formation of equiaxed grains in the thermomechanically affected zone (TMAZ) on the advancing side (AS). Additionally, the increment in tool rotational speed significantly improved the tensile strength, weld joint quality, and joint efficiency.

Microstructures and Mechanical Properties of Solid-State Welded Steels

This study aimed to evaluate the soundness of solid-state welded steels. STS 430F alloy with a rod type was selected as experimental material, and the friction welding was conducted at a rotation speed of 2,000 RPM and upset length of 3 mm. The application of friction welding on STS 430F rods led to significant grain refinement in the welded zone (1.3 µm) compared to that observed in the base material (16.8 µm). The refined grains in the welds contributed to the development of the mechanical properties. In particular, the Vickers microhardness was increased by approximately 25% compared to the base material, and the fracture at the tensile specimen of the welds occurred at the base material zone and not in the welded zone, which suggests a soundly welded state on the STS 430F rods.

In-Situ Hollow Sample Setup Design for Mechanical Characterisation of Gaseous Hydrogen Embrittlement of Pipeline Steels and Welds

This work discusses the design and demonstration of an in-situ test setup for testing pipeline steels in a high pressure gaseous hydrogen (H2) environment. A miniature hollow pipe-like tensile specimen was designed that acts as the gas containment volume during the test. Specific areas of the specimen can be forced to fracture by selective notching, as performed on the weldment. The volume of H2 used was minimised so the test can be performed safely without the need of specialised equipment. The setup is shown to be capable of characterising Hydrogen Embrittlement (HE) in steels through testing an X60 pipeline steel and its weldment. The percentage elongation (%El) of the base metal was found to be reduced by 40% when tested in 100 barg H2. Reduction of cross-sectional area (%RA) was found to decrease by 28% and 11% in the base metal and weld metal, respectively, when tested in 100 barg H2. Benchmark test were performed at 100 barg N2 pressure. SEM fractography further indicated a shift from normal ductile fracture mechanisms to a brittle transgranular (TG) quasi-cleavage (QC) type fracture that is characteristic of HE.

Hydrogen Induced Cracking Damage Estimation and Evaluation

New non-destructive testing (NDT) inspection technology, quantification of damage, and tensile testing, has enabled the assessment of conservatism associated with the hydrogen induced cracking (HIC) damage parameter (DH) currently used in API 579 – 1/ASME Fitness-For-Service (FFS) Part 7. To address HIC damage from an FFS perspective, the general requirements include addressing protection against plastic collapse and protection against cracking. The focus of this body of work is only to address conservatism regarding the protections against plastic collapse. The detrimental effects of HIC damage on plastic collapse is modeled through the DH parameter, currently set at 0.8 or an 80% strength loss in HIC damage material for the Level 2 HIC Assessment Procedure. Original development of the DH parameter was based on tensile testing of HIC damaged material performed in air, where the HIC damage was not sized or quantified, and a 30% margin was added to the maximum measured reduction in tensile strength to get to the 80% strength loss. Modification of the DH parameter is allowed in the Level 3 HIC Assessment Procedure, provided supporting testing data justifying a reduction is also provided with the assessment. For the tensile testing in air, the quantified HIC damage and tensile testing results are consistent with an 80% strength loss, without an added margin. A rigorous ultrasonic testing inspection using conventional phased array ultrasonic testing (PAUT) and PAUT with full matrix capture using the total focusing method (FMC/TFM) was performed on ex-service SA-212 Grade B material. Locations with service generated HIC damage were extracted and tensile tested in air and in gaseous hydrogen. Examination of the tensile specimen fracture surfaces allowed for quantification of HIC damage associated with final tensile failure. HIC damage measured with NDT was similar to the HIC damage on the fracture surface when characterized using the crack sensitivity ratio (CSR). The hydrogen tensile testing results suggested that for material still charged with hydrogen (not currently explicitly addressed in API 579 – 1/ASME FFS Part 7), the loss in strength may be larger than 80%.

Innovative bond strength testing of tin-based alloys for sliding bearings on steel supports

Since the bonding strength of Babbit alloys to their steel support cannot be measured with Chalmers specimens according to DIN ISO 4386, part 2, if the layer is too thin, an alternative specimen constellation was developed which enables the measurement of the bonding strength of layers as thin as 0.5 mm. The new specimen geometry consists of two coaxially aligned steel cylinders of equal diameter which leave a gap between opposite faces. After pretreatment in a metallic immersion bath of tin or an alloy of tin with 50 wt.-% zinc, the Babbit alloy is poured into the gap. Then the bonded steel cylinders are tensile tested. The force at fracture is divided by the cylinder cross-section yielding the bonding strength. This configuration is termed the face tensile specimen and was successfully tested on three different Babbit alloys. Up to a layer thickness of 1.5 mm the face tensile specimen delivers bonding strength quite comparable to those achieved with Chalmers specimens. Face tensile specimens require less Babbit alloy and are less costly to manufacture.

Optimization of Manufacturing Parameters and Tensile Specimen Geometry for Fused Deposition Modeling (FDM) 3D-Printed PETG

Additive manufacturing provides high design flexibility, but its use is restricted by limited mechanical properties compared to conventional production methods. As technology is still emerging, several approaches exist in the literature for quantifying and improving mechanical properties. In this study, we investigate characterizing materials’ response of additive manufactured structures, specifically by fused deposition modeling (FDM). A comparative analysis is achieved for four different tensile test specimens for polymers based on ASTM D3039 and ISO 527-2 standards. Comparison of specimen geometries is studied with the aid of computations based on the Finite Element Method (FEM). Uniaxial tensile tests are carried out, after a careful examination of different slicing approaches for 3D printing. We emphasize the effects of the chosen slicer parameters on the position of failures in the specimens and propose a simple formalism for measuring effective mechanical properties of 3D-printed structures.