Salman Khan

Joining of Austenitic Stainless Steel (AISI 304L) and Inconel (IN718) with Copper (Cu) interlayer was carried out using diffusion bonding. The bonding process was performed at bonding temperature of 950 °C for 90 min of holding time under 5 MPa of bonding pressure. The resultant bonding interface was investigated for its microstructural, compositional, and nanomechanical characteristics using optical and scanning electron microscopy (OM and SEM) with energy dispersive spectroscopy (EDS), and nanoindentation. The results reveal that the microstructure of AISI 304L was comprised of an equiaxed austenitic matrix with annealed twins while IN718 was comprised of annealed twins along with the formation of MC and M ₂₃ C ₆ carbides. Additionally, the maximum nanohardness occurred at the bonding interface (3.42 GPa) and AISI 304 BM (3.13 GPa) in the Cu/IN718 and Cu/AISI 304L respectively. Moreover, AISI 304 BM has highest elastic modulus (223 GPa) at the Cu/AISI 304 bonding interface while at the Cu interlayer (141 GPa) in the Cu/IN718 bonding interface. Lastly, average values of H/E _r and h _c /h _m reveals the pile-up behaviour around all the nanoindents.

The joining of Austenitic Stainless Steel (AISI 316) and Inconel (IN718) was carried out using Metal Inert Gas (MIG) welding and hybrid TIG-MIG welding with Inconel (IN625) and steel fillers. The resulting weldments were examined for their microstructural and compositional characteristics, elastic modulus, and nano-hardness using optical microscopy, X-ray diffraction, and nanoindentation techniques. The results indicated that the base metal IN718 exhibited higher hardness and elastic modulus compared to AISI 316. Additionally, the formation of the δ-Ni3Nb phase was observed in both MIG and hybrid welding processes using IN625 filler, along with austenitic matrices of Fe and Ni. When steel filler was used, it led to the development of a finer cellular, columnar, and equiaxed dendritic microstructure compared to the IN625 filler. The highest hardness in the heat-affected zone (HAZ) of IN718 was observed in hybrid welding with the steel filler, which was 7% and 5% higher compared to MIG welding with IN625 and steel fillers, respectively. Moreover, the maximum hardness in the fusion zone (FZ) of 4.55 GPa was achieved in MIG welding with the steel filler, which was 36% and 69% higher compared to hybrid welding with steel and IN625 fillers, respectively. The hardness varied between 2.74 GPa and 3.62 GPa in the HAZ of AISI 316 for MIG welding with steel and IN625 fillers, respectively. The elastic modulus was found to be 213 GPa in MIG welding with IN625 filler and 214 GPa in hybrid welding with steel filler. Pile-up behavior was observed around the nanoindents for all weldments obtained in both MIG and hybrid welding using steel and IN625 fillers.

Diffusion bonding of Inconel 718 (IN718) and Austenitic Stainless Steel (AISI 304L) was performed at 950 °C for 90 minutes of holding times under 5 MPa of bonding pressure. The resultant joint interface was investigated for its microstructural and compositional analysis, nano hardness, elastic modulus, and indentation creep. The result reveals that the joint interface was comprised of NbC, Cr ₂₃ C ₆ , and δ-Ni ₃ Nb along with the austenitic matrix of Ni and Fe. Similarly, a nanohardness of 3.5 GPa occurred at the bonding interface, which was 10% and 33% higher as compared to the base metals (BM) of IN718 and AISI 304L, respectively. Additionally, a minimum elastic modulus of 190 GPa was achieved at the AISI 304L BM as compared to other bonding zones (BZ). Moreover, a creep deformation of 73 nm occurred at the bonding interface and the stress exponent of bonding interface was 17% and 57% lower as compared to AISI 304L and IN718 BM respectively. Lastly, the bonding interface has higher creep resistance compared to other BZ and pile-ups were appears around the nanoindents in all bonding zones as analyzed with atomic force microscopy (AFM).

Diffusion bonding of aluminum alloy (AA-7075) with austenitic stainless steel (AISI 304L) was performed in the environment of Argon inert gas. The resultant bonding interface was investigated for its mechanical, nanomechanical, microstructural, and compositional characteristics using lap shear tests, nanoindentation and indentation creep, as well as optical (OM) and scanning electron microscopy (SEM), with energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The results revealed that intermetallic compounds (IMCs) of FeAl ₃ , FeAl ₂ , FeNi ₃ , and Fe ₃ Ni ₂ were formed at the bonding interface. Similarly, a nano hardness of 3.5 GPa occurred at the bonding interface which was 15% and 454% higher as compared to base metal (BM) of AISI 304 and AA-7075 respectively. Additionally, indentation creep showed that the bonding interface has higher creep resistance compared to other bonding zones (BZ). Lastly, an average shear strength of 67 MPa was achieved with a joint efficiency of 58%.

Exhaust components combining Inconel and stainless steel offer the most cost-effective hybrid design for high-performance engines. Owing to the formation of brittle compounds, the most critical zone in such components is the joint interface, which must have a suitable creep life. The present study investigated the nano creep and nanomechanical behavior of diffusion-bonded Austenitic stainless steel (AISI 304) and Inconel (IN-718) with a Cu interlayer. Maximum nano hardness of 3.25 GPa in AISI 304 and 3.12 GPa in IN-718 was achieved at the Cu/IN-718 and Cu/AISI 304 interfaces, respectively. Additionally, the least elastic modulus of 159 GPa in the Cu interlayer, and 160 GPa in the bonding interface was occurred at the Cu/IN-718 and Cu/AISI 304 interfaces, respectively. Moreover, the creep displacement of the Cu/AISI 304 interface was 327% higher than that of the Cu/IN-718 interface. Lastly, the Cu/IN-718 interface exhibited diffusional creep, while the Cu/AISI 304 interface exhibited both diffusional and dislocation creep as active mechanisms.

Diffusion bonding (DB) of Inconel (IN718) with Austenitic Stainless Steel (SS-304L) was conducted by varying the bonding temperatures and times at 5 MPa of pressure under vacuum. The optimized joint interface was evaluated for its mechanical, nanomechanical, microstructural, and compositional analyses using shear and Vickers hardness tests, optical and scanning electron microscopy (OM & SEM) equipped with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and nanoindentation. The results showed that the optimized bonding parameters for achieving a stable joint interface were 950 °C for 90 min of holding time. It was observed that the joint interface was comprised of NbC, Cr ₂₃ C ₇ , Fe ₂ Nb, and δ-Ni ₃ Nb. The maximum nanohardness of 3.5 GPa occurred in the joint interface which was 10% and 35% higher as compared to the base metals (BM) of IN718 and SS-304L, respectively. Lastly, maximum joint strength of 143 MPa was achieved with a joint efficiency of 37%.

Mass and heating rates alter the thermal properties, molecular structure, and phase changes of the materials. This study aimed to investigate the influence of sample mass (10-30 mg) and heating rate (4-15 °C/min) on the thermal characteristics of high-density polyethylene (HDPE) using differential scanning calorimetry (DSC). The experiments were conducted in two cycles. In the first cycle, samples of different masses (10-30 mg) were heated to 180 °C followed by cooling at a constant heating rate of 10 °C/min with a mass flow rate of 20 ml/min of purging gas (nitrogen). In the second cycle, a sample mass of 15 mg was used to investigate the thermal characteristics while varying the temperature rates (4, 6, 8, 10, and 15 °C/min). It was concluded that the variation in sample mass significantly affected the thermal properties of HDPE, leading to a slight increase in the melting temperature and latent heat, which shifted towards higher temperatures. In contrast, the temperature rate caused a reduction in the latent heat and crystallization temperatures. The thermograms obtained from the experiments provided insight into the thermal behavior of HDPE under different conditions, and the findings emphasized the importance of carefully considering the effects of mass and temperature rate when measuring the thermal properties of HDPE.