The influence of the consolidation route on the microstructure and high-temperature oxidation behaviour of the non-equiatomic Fe1.5Cr1Al0.75Mo0.1Ti0.1Ni0.25 multi-principal element alloy (MPEA6) was systematically investigated. Samples were fabricated by casting, Spark Plasma Sintering (SPS), and Electric Resistance Sintering (ERS) in order to isolate processing-induced effects while preserving constant composition. Although all routes preserved the BCC-B2 phase constitution, significant differences were observed in grain size, precipitate morphology, and structural homogeneity. Spark Plasma Sintering allowed controlled grain refinement and tuning of B2 precipitate size through adjustment of sintering conditions, whereas ERS produced ultrafine B2 precipitates (30-40 nm) but introduced intrinsic porosity gradients. Hardness measurements revealed a competition between grain boundary strengthening and precipitation strengthening, reflecting the combined influence of grain size and B2 dispersion. Oxidation tests at 800 degrees C for 48 h showed that the SPS-processed condition with refined and homogeneous microstructure developed thinner and more uniform oxide scales compared to the cast alloy. These results demonstrate that oxidation resistance in MPEA6 is governed not only by nominal composition but also by the processing-controlled microstructural state. Processing, therefore, emerges as a key design parameter to tailor both mechanical and environmental performance in Al-containing MPEAs.
This study investigates the effect of secondary vanadium carbide (VC) on the mechanical properties and wear behaviour of TiC-Ni cermets. The cermets were fabricated from TiC, Ni, and 1, 3, and 5 vol% VC, while the nickel content was fixed at 5 vol%. Spark plasma sintering (SPS) was carried out at 1280 degrees C under an applied pressure of 50 MPa for 8 min. The relative density of the VC-free sample reached 97.41% and increased to above 98% with VC addition. Phase analysis indicated a significant reduction in free nickel with increasing VC content. Microstructural observations revealed the formation of a grey interfacial region in SEM images, accompanied by a decrease in free Ni and isolated TiC grains. Hardness increased from 15.34 GPa for the VC-free cermet to 16.71 GPa for the sample containing 5 vol% VC. Fracture toughness showed a moderate increase from 7.20 MPa & centerdot;root m to 7.61 MPa & centerdot;root m with VC addition. Wear tests demonstrated a pronounced reduction in wear rate, decreasing from 8.6 & times; 10- 3 mg & centerdot;m- 1 for the VC-free sample to 4.2 & times; 10- 3 mg & centerdot;m- 1 for the cermet containing 5 vol% VC. These results suggest that secondary VC addition improves densification and microstructural characteristics, resulting in enhanced mechanical performance and wear resistance.
This study detailed the optimisation of process parameters for the laser powder bed fusion (LPBF) additive manufacturing process to produce crack-free, high-density M2 high-speed steel alloy. The high carbon content of this steel increases its susceptibility to cracking under the steep thermal gradients of the LPBF process. The work identifies optimised processing parameters for manufacturing defect-free M2 high-speed steel with minimal residual stress. A matrix of samples was built by varying laser power and scan speed, under 180°C platform heating. It was found that there are three distinct sample behaviours, categorised by volumetric energy density (VED): build failure at high energy density, macro-cracking at intermediate energy density and sound but porous structures at low energy density. X-ray diffraction analysis of cracked samples revealed phase transformations with varying VED, suggesting that the thermal gradient played a significant role in crack formation. While analysing the set of samples without visible macro-cracking, a critical VED of 27 J/mm 3 was identified, resulting in a crack-free sample when using a relatively low power (225 W) and low speed (1000 mm/s) combination, which reduces thermal stress. Using this optimal baseline, the process was further refined by adjusting the laser hatch distance. Decreasing the hatch distance from 140 µm to 120 µm successfully minimised internal porosity by promoting ideal melt pool overlap. The optimised process yielded fully dense, crack-free parts with a relative density of 99.38% (8.11 g.cm −3 ) and an as-built hardness of 643 HV0.5.
To meet the growing demand for fine-particle-size, high-performance 316L stainless steel powder in additive manufacturing, the coupled effects of atomization pressure (3–8 MPa) and delivery tube extension length (−2 to +2 mm) on the gas atomization dynamics are investigated. Using computational fluid dynamics (CFD) coupled with experimental validation, the flow-field characteristics and particle size distribution in a close-coupled atomization configuration are analyzed. The results reveal that the aspiration pressure (ΔP) exhibits a non-monotonic trend with increasing pressure, reaching a minimum (−28 641.8 Pa) at 4 MPa and becoming positive beyond 6 MPa, which suppresses melt outflow and poses a risk of nozzle clogging. Tube extension elevates the flow velocity but markedly increases ΔP; for example, at 4 MPa, lengths exceeding +1 mm lead to a positive ΔP. Using ΔP < 0 as a stability criterion, a quantitative stable processing window is defined. Within this window, simultaneously increasing the pressure and employing moderate tube extension synergistically refines the powder and narrows the particle size distribution. The simulation predictions show good agreement with experimental data (an average error of 4.7% for D 50 at 4.5 MPa). This work provides a theoretical foundation and a practical processing window for producing high-quality 316L stainless steel powder.
Pressureless liquid-phase sintering of Cu containing a mechanically milled 28Cu–72Ag (wt.%) premix was investigated to relate premix content and thermal history to densification, microstructure, hardness and electrical conductivity. Cu blends containing 0–40 wt.% premix were processed using five schedules that varied heating rate and holding time. Increasing premix content enhanced densification despite lowering green density. D120–Cu–40Et gave the largest mean relative density ( ∼ 93.4%), while H20–Cu–40Et reached ∼ 92.2% after 15 minutes at 800 °C. Longer high-temperature exposure refined pores and increasingly rounded Cu-rich regions at higher premix contents, whereas rapid heating retained finer, heterogeneous Ag-rich intergranular regions. X-ray diffraction and energy-dispersive spectroscopy identified mutually soluble Cu-rich and Ag-rich face-centred-cubic phases without additional crystalline intermetallics. When combined hardness and conductivity are prioritised, with density and hold duration as trade-offs, H20–Cu–40Et is the single recommended tested condition: (67.9 ± 2.3) HV 0.1 and (77.9 ± 2.0)% IACS. D120–Cu–40Et is the density benchmark, not a second overall optimum; the recommendation is based on observed means without significance testing.
