Papers by Keyword: Porosity

Abstract: High strength 7xxx series aluminium alloys are widely utilized in the aerospace, automotive and other manufacturing industries due to their low cost, high specific strength, high stiffness strength and fracture toughness. Additive manufacturing presents new opportunities in producing 7xxx series aluminium alloys such as reduced material waste, shorter lead time, and increased design freedom. This paper reviews the current progress in Wire Arc Additive Manufacturing (WAAM) of 7xxx series aluminium alloys, a technology that offers benefits such as better energy absorption than alternative laser-based processes, high deposition rates, and unrestricted build size. A classification of the AM processes utilized to fabricate aluminium alloys and WAAM process variants for fabricating aluminium alloys are introduced. Also, some common defects including porosity, solidification cracking and volatile elements loss encountered during the WAAM process of 7xxx series aluminium alloys are discussed. Whilst porosity remains a major issue in 7xxx series aluminium alloys produced via WAAM, several opportunities to minimize or eliminate the defects through process selection and alloy development are presented.

Abstract: In this research, a NiCrMoFeCoAl-30%Cr3C2 composite finish was deposited using an HVOF technique on the T22 bare steel. Cr3C2 coatings provide excellent durability and corrosion resistance. When manufacturing homogenous and dense Cr₃C₂ layers with decreased as-deposited greater hardness, surface roughness, and enhanced quality corrosion resistance, high-velocity oxy-fuel spraying with suspension feedstock has been a viable choice. Scanning electron microscopy with energy dispersive spectroscopy and X-ray diffraction have been used to examine the specimen's microstructure. Coating properties such as thickness, microhardness, and porosity were measured.

Abstract: Scaffold Carbonated Hydroxyapatite/Honeycomb/Polyethylene Oxide (CHA/HCB/PEO) has been obtained by freeze-drying. The bioceramic CHA used in this study was synthesized from oyster shells using precipitation. HCB and PEO were added as reinforcement materials that affect the crystallographic properties of the scaffold. This study aimed to determine the characteristics of the scaffolds for bone tissue engineering. CHA and scaffolds were characterized using Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffractometer (XRD), and Scanning Electron Microscopy (SEM). FTIR spectra and XRD graphs confirmed that the CHA produced was B-type. FTIR spectra of the scaffold showed the presence of HCB and PEO in the scaffold, which means they were homogeneously bound in the scaffold solution. XRD test results show that scaffolds' crystallinity and crystallite size tends to decrease compared to CHA. This was good because they could make cells easier to proliferate. A small-scale pore structure (micropore) was also formed in the scaffold. The porosity and pore size of the scaffold were affected by the concentration of CHA. The presence of the micropores can increase the permeability of the scaffold and facilitate cell migration. Thus, the composition of CHA/HCB/PEO scaffolds can be a good candidate material in bone tissue engineering.

Abstract: The solidification mechanism of ductile iron is a bit complex due to the precipitation of graphite and silicon. These elements change the solidification pattern of cast iron. Density of these elements is less than iron leads to occupying more volume consequently increase the overall metal volume. There are two aspects on this increase in metal volume. One is, reducing this volume increase to reduce the creation of porosities at the earlier stage of solidification and second is, using this volume increase to remove porosity at the later stage of solidification. Proper understanding of this graphite expansion in cast iron solidification will bring insights on reducing or removing of the risers. The current study focus on correlating the net contraction and austenitic liquidus point with shrinkage. The average contraction found through this study is 1.36 % which is more than the net expansion of 0.25 % (without riser) reported in literature.

Abstract: The plasma sprayed bronze coatings are widely used for repairing of plain bearing used in different applications. This type of coating was not deeply analyzed in state-of-art publications. In presented article we fill this gap in the case of plasma spraying process. The influence of power current (300/500/700A) and hydrogen flow (0/4/8 NLPM) on microstructure and thickness of aluminium bronze-polyester coating was investigated. The Thermico A60 plasma torch was used for thermal spray process of coating on flat carbon steel samples (grade S355). The Metco 604NS was sprayed with 20g/min powder feed rate. The obtained results showed the presence of local large pores formed by burning of polyester in plasma plume. This gap makes role of oil pockets in bearings. The obtained coatings were characterized by large deviation in thickness in range 200-350 micrometers. It might be concluded that in requires additional milling process after deposition.

Abstract: Sintered Ti6Al4V titanium alloys prepared from TiH₂/60Al40V powder blends under various technological conditions were studied. The microstructural evolution was investigated by X-ray diffraction, scanning electron microscopy, optical microscopy, and energy dispersive X-ray analysis. The corrosion resistance of sintered titanium alloy was evaluated by the static immersion test in 40 wt.% H₂SO₄ acid, according to ASTM standard G31-72(2004). Depending on powder metallurgy processing parameters (compaction pressure or sintering temperature), the Ti6Al4V alloy was obtained with various structural features (porosity and structural heterogeneity). It was shown that those structural features of sintered Ti6Al4V titanium alloy are a key microstructural factor that determines their corrosion resistance. For instance, an increase in porosity leads to enhanced corrosion resistance. Based on the current research, the optimal manufacturing regimes of powder metallurgy of Ti6Al4V titanium alloy ensure the achievement of characteristics sufficient for practical use in aggressive conditions of the chemical industry were obtained.

Abstract: The main theoretical aspects of porous and powder materials technological processing is worked out. The proposed material model is based on: - the four-parameter plasticity theory, which reflect the influence of porosity, resistance and the presence of dilatancy of solid phase deformation regime; - the dissipative potential and the load surface expression, that allow to take account such materials elastic - viscous - plastic properties; - the solid phase energy deformation speed with its subsequent over the representative element volume averaging. The peculiarity of this model is that the equilibrium flow concept elastic-viscous-plastic material is an alternative to its elastic-plastic deformation. The proposed equations are suitable for their effective practical using for digital models creation that based on existent software for the of equilibrium processes of compact materials deformation finite–element analysis. The practical use of the proposed methodologies made it possible to determine: - the regularities of the different modules material layers interaction during stamping of bimetallic blanks with an conical working surface; - the porosity distribution over the product volume at the final stage of radial extrusion of the bushings with an internal flange; - the effect of powder material decompression during reverse extrusion of cylindrical products.

Abstract: We report the fabrication of porous hydrophobic flat sheet membranes composed of polyvinylidene fluoride-co-hexafluoropropylene (PVDF-co-HFP), which is incorporated with graphene (GNP) concentrations of (0.2, 0.5, and 0.8 wt.%) as the hydrophobic filler. FTIR, XRD, and SEM results were used to analyze the composites' functional groups, crystallinity and surface morphology. The water contact angles were 116 ±1.2°; 120 ±0.9°; 126 ±0.7°; 130 ±0.6° for pristine, 0.2 wt%, 0.5 wt%, and 0.8 wt% of GNP membranes, respectively. Moreover, the graphene incorporation enhanced the fabricated polymer's ultimate tensile strength (UTS). The UTS was as follows 2.4±0.01, 5.43±0.02, 7.485±0.015 and 6±0.01MPa for pristine, 0.2 wt% GNP, 0.5 wt% GNP and 0.8 wt% GNP respectively. The highest UTS was (7.485 ±0.015 MPa) for the 0.5 wt% GNP. Graphene incorporation (0.5 wt%) enhanced the membranes’ porosity (78 ±1.9%). This study explored the effect of graphene to improve the flat sheet membranes' mechanical strength, hydrophobicity, and porosity, which can then be applied in desalination using membrane distillation to mitigate clean water shortages and crises.

Abstract: Dynamic modulus vs. temperature was measured in different alloys (stainless steels, Al alloys, Ti alloys, Ni-base superalloys) prepared by additive manufacturing and an anomalous trend was observed in some of them. Dynamic modulus, measured in successive mechanical spectroscopy test runs with heating-cooling cycles, exhibits an anomalous trend in the first test run that is no longer present in the successive runs. The phenomenon consists in the inversion of the decreasing trend of modulus occurring during heating and gives rise to its permanent increase at the end of the complete heating-cooling cycle. The temperature range where the modulus anomaly takes place and the permanent increase observed after cooling depend on the specific alloy. Scanning electron microscopy (SEM) observations and density measurements revealed that the irreversible process causing the anomalous behavior is the closure of pores of nanometric size leading to material densification. This result has been discussed by considering lattice diffusion.

Abstract: This investigation estimated porosity and dislocation density in austenitic stainless steel 316LSi thin walls fabricated by Cold Metal Transfer Wire and Arc Additive Manufacturing (CMT-WAAM). Porosity density was calculated using ImageJ software. MAUD software (Materials Analysis Using Diffraction) was used to analyze the microstructural parameters and dislocation density. The density of pores and microstructural parameters of 316LSi alloy exhibit typical values of AM conditions. The porosity values oscillate between 2.80 to 3.48 %. The obtained dislocation density values are 5.0 e+12, 4.3 e+12, and 3.2 e+12 for 2.4 e+12 m^-2 for 70, 80, 90, and 140 A current source, respectively. In 316LSi thin walls, the increases in the current input in CMT-WAAM are accompanied by the very lowest decrease in the dislocation density state.