Revisiting fundamental welding concepts to improve additive manufacturing: From theory to practice

Selective laser melting (SLM) and laser cladding deposition (LCD) are two typical kinds of laser additive manufacturing techniques that have been developed for many years independently. Although they are based on the same principle of laser cladding, there are little comparison on the fundamental studies for metallurgical behavior (including melting and solidification behaviors) and the mechanical properties of these two techniques up to now. In this paper, the single-track formation and the deposition of block sample from 316L stainless steel powders have been carried out by both SLM and LCD techniques. A comparison on pool shape, cooling rate, columnar grain size and mechanical properties under different processing conditions by LCD and SLM respectively has been studied. It is found that, due to the increase of energy input and the decrease of depth-to-width ratio of melting pool (MP) from SLM to LCD, the primary cellular arm spacing (PCAS) of the sample increases from less than 1.0 µm to more than 15.0 µm, and thus the cooling rate of MP decreases from about 106 K/s in SLM to about 102 K/s in LCD. Furthermore, due to the decrease of cooling rate from SLM to LCD, the columnar grains of the as forming alloy are getting coarser. Especially, the relationship between gain size (λ) and the reciprocal of square root of cooling rate ( T ) in LCD significantly meets the classical linear function of λ = a + b / T (a and b are constants), while a new relationship of a cubic function is found in SLM, showing the different solidification characteristics between LCD and SLM. Lastly, the samples of 316L stainless steel by SLM have much stronger tensile strength but lower elongation than those by LCD, and the main reason is due to that the solidification behavior of the MPs by SLM can form much finer columnar grains than those by LCD.

A comparison on metallurgical behaviors of 316L stainless steel by selective laser melting and laser cladding deposition

Effect of energy input on microstructural evolution of direct laser fabricated IN718 alloy

Effect of base metal and welding speed on fusion zone microstructure and HAZ hot-cracking of electron-beam welded Inconel 718

Online monitoring of thermo-cycles and its correlation with microstructure in laser cladding of nickel based super alloy

The effect of heat input from laser beam welding (LBW) on the microstructural evolution of superalloy Inconel 718 was investigated. LBW was carried out on 1.6-mm-thick sheets with an average grain size of 13 μm (ASTM # 9.5), and four different heat inputs in the range of 74.5 mm−1 to 126.6 J mm−1 were used. Full penetration was achieved in all weld experiments. Microstructures of the welds were evaluated using an optical microscope and a field emission scanning electron microscope. Increasing the heat input changed the resulting weld shape from a wine glass shape to a stemless glass shape with wider surface bead widths, and the measured average dendrite arm spacing was increased from 1.06 μm to 2.30 μm, indicating the corresponding solidification rate in the range of 1.75 × 105 K s−1 (°C s−1) to 3.5 × 106 K s−1 (°C s−1). The welds also were free from microfissuring even at the lowest heat input trials. The Nb concentration of Laves phase for the current LBW samples was ≈20.0 wt pct. The coefficients of partition and distribution for Nb were determined to be approximately 3.40 and 0.50, respectively.

A Study on Laser Beam Welding (LBW) Technique: Effect of Heat Input on the Microstructural Evolution of Superalloy Inconel 718

A self-flowing low-cement bauxite castable was prepared from 64 wt.% rotary Chinese bauxite and 10 wt.% Eczacibasi calcined alumina aggregates with additives of 5 wt.% Lafarge cement Secar 71, 8 wt.% Elkem microsilica 971U, and 0.05 wt.% dispersant Darvan 7S (D7S). Optimum self-leveling flowability was achieved using 5.6% water addition. As a function of the firing temperature, the physicomechanical and refractory properties of the self-flowing low-cement bauxite castable were characterized in terms of densification parameters such as apparent porosity (AP), bulk density (BD), water absorption (WA), and cold crushing strength (CCS). Phase analysis and microstructural-based evaluation were performed using x-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The present bauxite-based refractory castable heat treated at 1500°C for 2 h exhibited the following properties: AP 13%, BD 2.93 g/cm3, WA 4.4%, and CCS 1365 kg/cm2.

Effects of firing temperature on the physical properties of a bauxite-based refractory castable

CO 2 laser butt-welding of Co-base superalloy Haynes 188 was performed on 2.1 mm-thick sheets with an average grain size of 21 μm (ASTM #8). Nine different heat inputs in the range of 61.3–90.1 J mm −1 were used. The corresponding solidification rates at the weld fusion zone were in the range of 2×10 3 to 1×10 4  °C s −1 . The distribution coefficients for the alloying elements in the laser beam welded samples were close to unity. The yield and tensile strengths, the strain hardening exponents, and the strength mismatch ratios decreased with increasing heat input. The corresponding joint efficiencies of the high and low heat input trials were 84% and 93%, respectively. Fractography analysis of the base material and laser beam welded sheets revealed dimple-like ductile fracture characteristics.

Assessment of the effects of heat input on microstructure and mechanical properties in laser beam welded Haynes 188 undermatched joints

A study on graphene reinforced carbon fiber epoxy composites: Investigation of electrical, flexural, and dynamic mechanical properties

type microsilica was developed. Optimum flow characteristics were achieved using water addition of 4?6 wt-%. This batch was sintered at different firing temperatures up to 1500uC. To understand the effect of both firing temperatures and corresponding phases, the present castable was characterised in terms of X-ray diffraction, scanning electron microscopy, bulk density (BD), apparent porosity (AP), water absorption (WA), cold crushing strength (CCS) and self-leveling flowability. The results revealed that gradual increase in firing temperature from 1100 through 1500uC caused low AP and WA, and high CCS properties due to the densification of the

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Papers

A Study on Laser Beam Welding (LBW) Technique: Effect of Heat Input on the Microstructural Evolution of Superalloy Inconel 718

Effects of firing temperature on the physical properties of a bauxite-based refractory castable

Assessment of the effects of heat input on microstructure and mechanical properties in laser beam welded Haynes 188 undermatched joints

A study on graphene reinforced carbon fiber epoxy composites: Investigation of electrical, flexural, and dynamic mechanical properties

Preparation and characterisation of self-flowing refractory material containing 971U type microsilica