Unlike conventional materials removal methods, additive manufacturing (AM) is based on a novel materials incremental manufacturing philosophy. Additive manufacturing implies layer by layer shaping and consolidation of powder feedstock to arbitrary configurations, normally using a computer controlled laser. The current development focus of AM is to produce complex shaped functional metallic components, including metals, alloys and metal matrix composites (MMCs), to meet demanding requirements from aerospace, defence, automotive and biomedical industries. Laser sintering (LS), laser melting (LM) and laser metal deposition (LMD) are presently regarded as the three most versatile AM processes. Laser based AM processes generally have a complex non-equilibrium physical and chemical metallurgical nature, which is material and process dependent. The influence of material characteristics and processing conditions on metallurgical mechanisms and resultant microstructural and mechanical properties of AM proc...

Laser additive manufacturing of metallic components: materials, processes and mechanisms

https://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1037&context=mepubs

Additive manufacturing of Ti6Al4V alloy: A review

A review on selective laser sintering/melting (SLS/SLM) of aluminium alloy powders: Processing, microstructure, and properties

This article reviews published data on the mechanical properties of additively manufactured metallic materials. The additive manufacturing techniques utilized to generate samples covered in this review include powder bed fusion (e.g., EBM, SLM, DMLS) and directed energy deposition (e.g., LENS, EBF3). Although only a limited number of metallic alloy systems are currently available for additive manufacturing (e.g., Ti-6Al-4V, TiAl, stainless steel, Inconel 625/718, and Al-Si-10Mg), the bulk of the published mechanical properties information has been generated on Ti-6Al-4V. However, summary tables for published mechanical properties and/or key figures are included for each of the alloys listed above, grouped by the additive technique used to generate the data. Published values for mechanical properties obtained from hardness, tension/compression, fracture toughness, fatigue crack growth, and high cycle fatigue are included for as-built, heat-treated, and/or HIP conditions, when available. The effects of test...

Metal Additive Manufacturing: A Review of Mechanical Properties

Titanium and nickel alloys represent a significant metal portion of the aircraft structural and engine components. When these critical structural components in aerospace industry are manufactured with the objective to reach high reliability levels, surface integrity is one of the most relevant parameters used for evaluating the quality of finish machined surfaces. The residual stresses and surface alteration (white etch layer and depth of work hardening) induced by machining of titanium alloys and nickel-based alloys are very critical due to safety and sustainability concerns. This review paper provides an overview of machining induced surface integrity in titanium and nickel alloys. There are many different types of surface integrity problems reported in literature, and among these, residual stresses, white layer and work hardening layers, as well as microstructural alterations can be studied in order to improve surface qualities of end products. Many parameters affect the surface quality of workpieces, and cutting speed, feed rate, depth of cut, tool geometry and preparation, tool wear, and workpiece properties are among the most important ones worth to investigate. Experimental and empirical studies as well as analytical and Finite Element modeling based approaches are offered in order to better understand machining induced surface integrity. In the current state-of-the-art however, a comprehensive and systematic modeling approach based on the process physics and applicable to the industrial processes is still missing. It is concluded that further modeling studies are needed to create predictive physics-based models that is in good agreement with reliable experiments, while explaining the effects of many parameters, for machining of titanium alloys and nickel-based alloys.

Machining induced surface integrity in titanium and nickel alloys: A review

A titanium-copper-nickel braze powder is combined with various carrier polymers at a range of loadings and used to braze open cell nickel foams to Ti–6Al–4V plate. The microstructure of the interfaces and the chemical composition are examined, and these are correlated with the mechanical behaviour of the joints, as determined by shear and tensile tests, with the aim being to determine the influence the polymer binder and application method have on the final bond microstructure and properties. The investigations show that, as expected, the binder system used can have an important effect on the amount of oxygen, carbon and nitrogen contained in the braze material, and the mechanical properties obtained. However, the effect is complex, better properties in shear being obtained with an apparently lower quality bond, an observation that is explained by considering the constrained boundary layer formed by the bond. Further Weibull tests show that, although the density variations in the commercially available nickel based foam affect the properties, there is additional variation due to the high degree of process control required to achieve a good bond.

The bonding of nickel foam to Ti–6Al–4V using Ti–Cu–Ni braze alloy

Simulated foreign object damage has been inflicted at room temperature on two competing titanium based materials destined for compressor aerofoil applications in future gas turbine engine designs. Laboratory specimens, manufactured in the conventional titanium alloy Ti–6Al–4V and the γ titanium aluminide Ti–45Al–2Mn–2Nb, were subjected to impacts of various energy, representative of severe in-service damage. Damage sites were fully characterised prior to subsequent fatigue assessment at both room temperature and elevated temperatures typical of the envisaged maximum working temperatures for each alloy. In terms of absolute fatigue endurance levels the γ aluminide offers the weaker response at room temperature, however, this system offers clear advantages in terms of temperature capability.

Characterisation of foreign object damage and fatigue strength in titanium based aerofoil alloys

Following an introduction on the use of titanium alloys for aeroengine applications, results are presented on the creep feed grinding of a beta titanium alloy Ti-25V-15Cr-2Al-0.2C wt.% (BuRTi) using vitrified bonded superabrasive wheels in a fractional factorial experimental design. Despite a general perception to the contrary, the range of titanium alloys in use is wide encompassing different alpha/near alpha, alpha/beta and beta designations, each with specific mechanical/physical properties. In terms of aeroengine use, there are seven or eight key alloys (or their equivalent) used globally with the trend for higher operating capability both in relation to temperature and stress level. In the experimental work, grinding forces were significantly lower with diamond; however, wheels employing CBN grits achieved the highest G-ratio (up to ~280) and lowest surface roughness (~0.73 μm of Ra). This was accompanied by workpiece smearing and surface burn, which was evident in the majority of tests using CBN. Additionally, workpiece softening was observed within the first 15 μm from the machined surface.

Creep feed grinding of burn-resistant titanium (BuRTi) using superabrasive wheels

Forming a hollow structure having an internal coating includes the steps of placing a core shaped to form the internal surface of the structure in a mould, filling the mould with a material powder, hot isostatically pressing the powder about the mould to consolidate the powder, and removing the core from the hollow structure formed, wherein a coating is applied to the core prior to placement in the mould, which coating bonds to the hollow structure formed, during the hot isostatic pressing, to form the internal coating.

HIP manufacture of a hollow component

XD ™ TiAl alloys are well known to have the advantage of a homogeneous microstructure when compared with monolithic TiAl-based alloys. In this research, however, an inhomogeneous microstructure consisting of a fully lamellar structure in the edge region and a duplex structure of equiaxed grains and lamellar colonies in the central area was discovered in as-HIPed Ti–45Al–2Mn–2Nb+0.8 vol.% TiB 2 bar. Electron probe microanalysis and optical/transmission electron microscopy of HIPed material, optical microscopy of cast material indicated the formation mechanism of the duplex structure in the central area was recrystallization due to the strain energy stored by the collapse of cast porosity during HIP. Crack initiation at the interface between regions of a duplex and a fully lamellar structure in high cycle fatigue testing suggested that the duplex structure might have a detrimental effect on the mechanical properties of the material.

Wayne Eric Voice

Papers

The bonding of nickel foam to Ti–6Al–4V using Ti–Cu–Ni braze alloy

Characterisation of foreign object damage and fatigue strength in titanium based aerofoil alloys

Creep feed grinding of burn-resistant titanium (BuRTi) using superabrasive wheels

HIP manufacture of a hollow component

Recrystallization in cast 45-2-2 XD titanium aluminide during hot isostatic pressing