An additive layer manufacture (ALM) technique, electron beam melting, has been used for the production of simple geometries, from prealloyed Ti-6Al-4V powder. Microstructure, texture, and mechanical properties achieved under standard operating conditions have been investigated. Three transitional regions are observed with a change in microstructural formation dependent on the thermal mass of deposited material. Prior b-phase reconstruction, from room temperature a-phase electron backscatter diffraction (EBSD) data, reveals a strong texture perpendicular to the build axis. Variation of build temperature within the processing window of 898 K to 973 K (625°C to 700°C) is seen to have a significant effect on the properties and microstructure of both as-deposited and hot isostatically pressed (HIP) samples.

Architectured materials comprised of periodic arrangements of nodes and struts are 11 lightweight materials that can exhibit combinations of properties which are inaccessible to 12 conventional solids. However, with regards to their mechanical performance, they have an 13Achilles heel in that these materials can exhibit a catastrophic post-yielding collapse, causing 14 substantial drops in strength and energy absorption during plastic deformation. This post-15 yielding collapse is the result of the activity of single shear bands, and originates from the single 16 orientation of macro-lattices. We observe that this behaviour is analogous to deformation by slip 17 in metallic single crystals. In this study we propose that, by mimicking the microstructure 18 observed in crystalline materials, we may be able to employ hardening mechanisms found in 19 crystalline materials to help us to develop robust and damage-tolerant architected materials. This 20 study demonstrates that crystal-inspired meso-structures can play as an important role in the 21 mechanical properties of architectured materials as do crystallographic microstructures in the 22 case of metallic alloys. Consequently, designing meso-structures that mimic crystallographic 23 microstructure in crystalline metals enables the fusion of metallurgy and architectured materials 24 to transform the way of designing a new type of materials with desired properties. 25 26 Main text references 363

a b s t r a c tAn Mg-7Sn-1Al-1Zn alloy known to have excellent extrudability and superior strength was subjected to artificial cooling during indirect extrusion by directly spraying water onto the extruded rod at the die exit. The results obtained revealed that this artificial cooling dramatically reduces the temperature of the deformation zone during extrusion, thereby creating a finer grain size, an intensified texture and a greater amount of precipitates when compared to extrusion without artificial cooling. The yield and tensile strength of the extruded alloy is also significantly improved, which is attributed to the effects of grain refinement in combination with an enhanced texture and precipitate hardening.

The Selective Laser Melting (SLM) process generates large thermal gradients during rapid melting of metallic powdered feedstock. During solidification certain alloys suffer from thermally induced micro-cracking which cannot be eliminated by process optimisation. An alloy's crack susceptibility may reduce by increasing its Thermal Shock Resistance (TSR), potentially achieved through an increase in tensile strength. This hypothesis is investigated with Hastelloy X, a common nickel-base superalloy of known high crack susceptibility when processing SLM. It is demonstrated that through consideration of the imposed rapid solidification conditions, Hastelloy X can be made to form a supersaturated solid solution in the as deposited state. The fundamental solid solution strengthening (SSS) effect is exploited to generate an increase in lattice stress, by increasing the most potent SSS elements present within the alloy, whilst maintaining specification composition. The modified alloy displayed a 65% reduction in cracking and an increase in elevated temperature tensile strength, lending support to the initial hypothesis and identifying a possible approach for developing further SLM crack resistant versions of well-known alloy compositions.

Without post-manufacture HIPing the fatigue life of electron beam melting (EBM) additively manufactured parts is currently dominated by the presence of porosity, exhibiting large amounts of scatter. Here we have shown that the size and location of these defects is crucial in determining the fatigue life of EBM Ti-6Al-4V samples. X-ray computed tomography has been used to characterise all the pores in fatigue samples prior to testing and to follow the initiation and growth of fatigue cracks. This shows that the initiation stage comprises a large fraction of life (>70%). In these samples the initiating defect was often some way from being the largest (merely within the top 35% of large defects). Using various ranking strategies including a range of parameters, we found that when the proximity to the surface and the pore aspect ratio were included the actual initiating defect was within the top 3% of defects ranked most harmful. This lays the basis for considering how the deposition parameters can be optimised to ensure that the distribution of pores is tailored to the distribution of applied stresses in additively manufactured parts to maximise the fatigue life for a given loading cycle.