Dissimilar welds between austenitic stainless steel Super304H and ferritic-martensitic steel T92 were produced using hot-wire gas tungsten arc welding employing ErNiCrFe-7A fillers. The welds were post-weld heat-treated (PWHT) at 760 °C for 2 h and subjected to creep testing at 650 °C and 120 MPa. The weld microstructures were characterized in detail in the as-welded, PWHTed, and crept conditions. The creep failures were observed to take place in the fine-grained heat-affected zone (FGHAZ) of alloy T92. Microstructural studies clearly revealed accelerated degeneration of martensitic lath structure, coarsening of chromium-rich carbides, and formation of detrimental Laves phase in the FGHAZ of alloy T92. The reasons for the accelerated microstructural degradation in the FGHAZ of alloy T92 are discussed in detail.

The compaction and sintering characteristics of silicon and a silicon composite containing a multi-component Molybdenum alloy (Mo 44 Si 26 Ta 5 Zr 5 Fe 3 Co 12 Y 5 ) as reinforcement is reported here. Compaction with different binders viz zinc stearate, stearic acid and poly-vinyl alcohol (PVA) revealed that only PVA is suitable for making crack free pellets. Furthermore, silicon particles with angular shape were found to develop cracks during compaction compared to those bearing spherical shape. The compaction characteristics of Si and Si composites were evaluated using the Heckel’s approach and analysis of data revealed that round particles ensure better die filling. Pressureless sintering of the silicon and silicon composite compacts was carried out at 1225 °C for a duration of 12 h and intriguingly the relative density of the sintered compacts was found to be lower than respective green compacts. This was attributed to poor sintering tendency of silicon and also to the loss of the volatile organic binder.

This study reports the effect of 650 °C exposure on microstructural evolution and creep behavior of post-weld heat-treated dissimilar welds between the alloys T92 and Super304H. The dissimilar welds were exposed for durations of 24 h, 100 h, 250 h, 500 h, and 1000 h to investigate the thermal stability of the microstructure. Creep tests were carried out at 650 °C and 120 MPa on the post-weld heat-treated and on 1000 h exposed dissimilar metal welds. The isothermal exposure degraded the microstructure of T92-HAZ, resulting in type IV failure at an accelerated rate under creep conditions. Further, accelerated recovery of martensitic laths and extensive precipitation of Laves phase on M23C6 carbides sitting at the grain boundaries of the fine-grained heat-affected zone (FGHAZ) during creep deformation were observed. The isothermal exposure on Super304H-HAZ showed no significant microstructural changes except precipitation of thick M23C6 carbides at the grain boundaries. These prominent microstructural changes in the HAZ of T92 lead to the accelerated void formation in the FGHAZ and are responsible for consequent premature failure.

Medium strength low alloy steel is an attractive material for naval and defence applications for its excellent mechanical properties. DMR 249A is extensively used for application of ship building for its superior mechanical properties but owes poor corrosion resistance. In order to overcome the corrosion problem, Weld overlay cladding is used as an effective technique which improves the strength and corrosion resistance but also helps in manufacturing lightweight structures. Aim is to combat the corrosion by weld overlay surface coating using conventional arc welding process and observe the dilution. In the current study, Weld overlay cladding on medium strength low alloy steel (DMR 249A) of 50mm thick is done using manual metal arc welding process (MMAW) with corrosion resistant austenitic stainless steel (308L) electrode. Two layers of coating were done one over the other (each 2mm thick). Weld overlay clads were characterized for metallographic studies to observe the microstructure changes using image analyzer attached to optical microscopy and scanning electron microscopy (SEM). Mechanical testing were carried out using micro vickers hardness tester andductility bend test using Universal Testing Machine (UTM). Pitting corrosion behaviour is determined by the potentio-dynamic polarization tests in acidic chloride environment. Inter Granular Corrosion (IGC) was performed in boiling copper sulphate solution as per ASTM A-262 for 15 hours duration. The present investigation established that microstructure studies revealed increase in δ-ferrite in the weld overlay cladding. Superior mechanical properties are observed in second overlay coating compared to first overlay coating and base metal. Pitting potential in second overlay coating is observed to be more positive when compared with first overlay coating due to increase in chromium content. IGC studies showed that first overlay coating with AISI 308L observed to be more sensitized and having more weight loss which tends to be highly susceptible than second layer coating. It is attributed to the formation of high amount of delta ferrite.

Hot deformation behavior of nickel-based superalloy XH 67 (Ni-18.5Cr-4.5Mo-4.5W-3.0Fe-2.5Ti-1.2Al) was investigated in the temperature range of 900 degrees C-1,200 degrees C and in the strain rate range of 10(-3)-10 s(-1). A processing map was generated from the flow stress data. Detailed postdeformation microscopy was carried out to understand the microstructural evolution during hot deformation. Correlation of the kinetic analysis together with microstructural characterization studies was accomplished to identify the rate controlling mechanism. An increase in the fraction of Sigma 3 boundaries is observed with an increase in the strain rate at 1,150 degrees C. In the temperature range of 1,100 degrees C-1,200 degrees C, discontinued dynamic recrystallization has been identified as the major softening mechanism. Based on the critical analysis of the mechanical data together with microstructural analysis, the safe hot working regime for the XH 67 alloy is established to have a temperature range of 1,100 degrees C-1,200 degrees C and a strain rate range of 10(-3) to 5 x10(-2) s(-1).

In this work, the role of grain boundary engineering (GBE) on the weld heat-affected-zone (HAZ) liquation cracking resistance of austenitic stainless steel AISI 316Ti was investigated. Standard wrought-processed alloy 316Ti was cold rolled to 5% strain and subsequently annealed at 1373 K for 30 min to achieve the optimum grain boundary character distribution (GBCD). The GBE samples were found to consist of a significantly higher fraction (72%) of low Sigma coincident site lattice (CSL) boundaries as compared to the as received (AR) samples (45%). To study the liquation cracking behavior, single-track longitudinal varestraint tests was performed on AR and GBE samples. Microstructural examination revealed that the grain coarsening and the liquation events were less prominent in the GBE samples as compared to the AR samples. It is believed that the reduced segregation of impurities to the special boundaries (coherent Sigma 3 twins, in particular) present in the GBE samples is responsible for the observed improvement in the HAZ liquation cracking resistance.

The hot deformation behaviour of two solid solution alloys Mg-3Al-3Sn (AT33) and Mg-3Al-3Sn-1 Zn (ATZ331) were investigated using processing maps approach, while elucidating the role of Zn. Processing maps were generated using the flow stress data from constant strain rate (10(-3) to 10 s(-1)) compression testing in the temperature range of 300 to 460 degrees C. Three distinct common domains (Domain I, II and III) were observed in the processing maps of AT33 and ATZ331. Addition of Zn is found to have expanded the domains range in ATZ331. Compared to AT33, an additional domain (Domain IV:T similar to 340 - 380 degrees C, (epsilon) over dot 10(-2) - 10(-1) s(-1)) is observed in ATZ331. The instability map showed instability regions in the temperature and strain rate range in which twinning was predominant. Rate controlling mechanisms were identified by correlating the activation energy (Q) and stress exponent (n) in individual domains. Flow softening mechanisms in individual domains are corroborated by correlating the post-deformed microstructures with the deformation mechanism. The Domain III (T similar to 400 - 460 degrees C, (epsilon) over dot = 1 - 10 s(-1)) is identified as the safe hot working regime for both the alloys AT33 and ATZ331 based on the correlation of microstructural evolution together with the processing maps and kinetic analysis. Dynamic recrystallisation is a dominant flow softening mechanism in Domain I, III and IV, whereas dynamic recovery is predominant in Domain II. On the whole, Zn addition has increased the tendency for cross-slip, and resulted in more recrystallisation in Domain I besides faster recovery in Domain II as compared to AT33.

High temperature creep testing at a very low load range (<10 N) on miniaturized specimens has always been a challenge due to inherent design limitation (such as significant preload) of the conventional creep testing machines. In the present study, the challenge was overcome by developing a simple and versatile horizontal creep testing machine to conduct creep tests in the loading range of ∼6-300 N in tension and in compression. The competence of the in-house-built horizontal creep machine was validated by conducting creep testing on dog-bone shaped sheet specimens of cast Mg-1Sn-1Ca (TX11) Mg-base alloy over a lower stress range of 1.6-5.9 MPa (equivalent load range of 6.4-18.1 N) at 450 °C and in the high stress range of 20-80 MPa (equivalent load range of 76-310 N) at 175 °C.

Friction surfacing is a candidate process for depositing corrosion and wear resistant coatings. Being a solid-state process, it offers several advantages over conventional fusion welding based surfacing process. In the current work, martensitic stainless steel AISI 410 was friction surfaced over mild steel substrates. Coating microstructures were characterized using light microscopy, scanning electron microscopy and Xray diffraction. Coatings in as-deposited condition exhibited a fully martensitic microstructure and were found to be quite hard (with an average hardness of 460 HV). Bend and shear tests indicated excellent coating/substrate bonding. Overall, the current work shows that martensitic stainless steel AISI 410 can be satisfactorily friction surfaced on mild steel.