AM Research Papers

Key finding: Comprehensive 92-page review establishing the physical mechanisms linking process parameters to melt pool dynamics, microstructure evolution, defect formation, and final mechanical properties across all metal AM processes.

Key finding: Systematic mapping of how the rapid thermal cycles in metal AM (cooling rates 10³–10⁶ K/s in LPBF vs. 10¹–10² K/s in EBM) drive columnar grain growth, texture, and anisotropy — and how post-processing mitigates these effects.

Key finding: Process–property relationships for the main metal AM processes, with emphasis on the role of scan strategy and energy density in controlling porosity and residual stress; demonstrates that LPBF can achieve wrought-equivalent tensile properties in optimised conditions.

Key finding: Meta-analysis of published tensile, fatigue, and fracture toughness data for AM metals; confirms that anisotropy, surface roughness, and porosity are the primary drivers of sub-wrought fatigue performance, and that HIP + machining can close most of the gap.

Key finding: Physics-based framework for LPBF melt pool dynamics; identifies three porosity regimes — lack-of-fusion (low VED), optimal, and keyhole (high VED) — and links them to Volumetric Energy Density with spatter and vapour depression mechanisms.

Key finding: Establishes the temperature gradient mechanism (TGM) and cool-down phase model that explains residual stress formation in LPBF. Derives the constraint factor C used in residual stress estimation: σ_res ≈ C × E × α × ΔT.

Key finding: Comprehensive review of LPBF process mechanisms. Establishes the VED-density relationship and identifies four densification mechanisms in PBF (complete melting, partial melting, full melting with balling, and solid-state sintering).

Key finding: LPBF Ti-6Al-4V solidifies as columnar prior-beta grains transforming to acicular alpha-prime martensite on rapid cooling, explaining the high as-built strength (~1100 MPa UTS) and low ductility (~6% elongation) relative to conventional Ti-6Al-4V.

Key finding: Comprehensive binder jetting review. ~15-22% linear shrinkage during sintering is inherent and must be compensated in CAD; sintered density >97% is achievable with optimised parameters.

Key finding: Systematic mapping of porosity in Ti-6Al-4V LPBF and EBM over a wide VED range; identifies the three-regime (LOF / optimal / keyhole) structure and shows that EBM produces more spherical pores at lower densities due to the pre-sintering step.

Key finding: As-built LPBF maraging 18Ni300 achieves hardness ~33 HRC (soft martensite); ageing at 480°C/6h raises it to ~54 HRC with <0.1% dimensional change — enabling the machine-then-age tooling workflow without distortion.

Key finding: Surface roughness and sub-surface pore size are the primary fatigue life drivers in LPBF; machining the surface alone can recover 60–70% of wrought fatigue performance, while HIP addresses internal defects for fracture-critical applications.

Key finding: CoCrMo EBM and LPBF parts show columnar FCC grains with ε-martensite (HCP) banding; solution annealing homogenises the structure and raises elongation from <5% to >20% while moderately reducing hardness.

Key finding: Solution annealing at 1150°C/1h transforms the as-built columnar dendritic structure of LPBF IN625 into equiaxed grains, nearly eliminating anisotropy; UTS remains ~900 MPa with elongation increasing from 28% to 45%.

Key finding: LPBF AlSi10Mg with 200°C preheat produces UTS ~400 MPa, YS ~230 MPa as-built; T6 (solution + aging) raises YS to ~240 MPa but reduces UTS due to coarsening of the Si network.

Key finding: LPBF 18Ni300 maraging steel aged at 480°C/6h achieves consistent hardness 52–54 HRC with <0.1% dimensional change — the dimensional stability during ageing is the key enabler for the machine-then-age tooling strategy.

Key finding: PA12 SLS part properties are highly sensitive to melt-pool temperature history; elongation at break is the most variable property (±50% across build volume) and correlates directly with the degree of crystallinity.

Key finding: Surface temperature homogeneity in the SLS powder bed (±5°C window) is the primary determinant of inter-layer bonding quality; thermal imaging enables real-time detection of cold zones that predict weak areas before build completion.

Key finding: PEEK SLS requires build chamber temperatures of 340–380°C (near melting point) to achieve adequate inter-layer bonding; at sub-optimal temperatures, delamination and poor crystallinity reduce tensile strength by >50% vs. injection moulding.

Key finding: Optimal PEEK SLS laser energy density produces crystallinity ~40% and UTS ~80 MPa, representing ~80% of injection-moulded PEEK; higher energy density causes yellowing (thermal degradation) without further strength gain.

Key finding: Reviews the full landscape of metal AM processes for aerospace. Identifies that the primary barriers to wider adoption are qualification and certification frameworks, not process capability — shifting the challenge from 'can we build it' to 'can we prove it'.

Key finding: Fatigue endurance of LPBF AlSi10Mg is ~97 MPa as-built and ~130 MPa after T6 + machining (R=-1, 10^7 cycles). As-built surface roughness and residual stress are the dominant fatigue limiters, not bulk porosity.

Key finding: Establishes the LPBF process window for AlSi10Mg achieving >99.5% density. As-built YS ~240 MPa, UTS ~330-360 MPa, elongation ~3-5% (XY). Key reference for AlSi10Mg as-built property ranges.

Key finding: Comprehensive aluminium LPBF review. The ultra-fine (~1 µm) Al-Si eutectic cellular network formed by rapid solidification is the primary strengthening mechanism, giving LPBF AlSi10Mg ~85% higher YS than die-cast equivalent.

Key finding: Surveys the state of DfAM research and identifies the critical gap between AM process capability and designer knowledge. Proposes a DfAM framework covering geometry freedom, process constraints, post-processing, and qualification.

Key finding: HIP improves LPBF Ti-6Al-4V fatigue life by ~30-50% by closing sub-surface pores. However, machined as-built specimens can match HIP + as-built surface specimens, suggesting surface finish is as important as porosity closure for fatigue performance.

Key finding: LPBF produces acicular alpha-prime martensite (high strength ~1100 MPa, low ductility ~6%) while EBM produces lamellar alpha+beta (lower strength ~800 MPa, higher ductility ~12%). EBM parts are nearly stress-free due to high preheat (600-700 deg C).

Key finding: LPBF CoCrMo achieves >99.5% relative density at optimal VED; as-built hardness of 40–44 HRC is acceptable for dental frameworks; demonstrated dimensional accuracy ±0.05 mm on crowns.

Key finding: DED-laser IN625 deposits show columnar dendrites aligned with build direction; post-HT at 1000°C triggers recrystallisation and δ-phase dissolution, improving toughness at the cost of moderate strength reduction.

Key finding: PA11 SLS inter-laboratory round robin shows inherent property scatter of ±8% in UTS and ±15% in elongation across facilities using identical parameters — demonstrating that PA11 SLS requires robust process control to achieve consistent ductility.