scispace - formally typeset
Search or ask a question

Showing papers by "S. Sankaran published in 2015"


Journal ArticleDOI
TL;DR: In this article, the authors used X-ray diffraction (XRD), transmission electron microscopy (TEM), and Raman spectroscopy characterization techniques to identify the presence of nickel deposition on the carbon nanotubes (CNTs) and the degree of graphitization.

52 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated the creep-fatigue interaction (CFI) behavior of 316LN stainless steel with varying nitrogen content (0.07, 0.14 and 0.22 ) at temperature of 873 K under strain-controlled fatigue tests with a tensile-hold period of 1, 13.3 and 30 min.

50 citations


Journal ArticleDOI
TL;DR: In this paper, electricalless copper coatings were performed on purified carbon nanotubes (CNT), with varying deposition time and the optimum deposition time in terms of uniform deposition was determined to be 45min.
Abstract: Electroless copper coatings were performed on purified carbon nanotubes (CNT), with varying deposition time and the optimum deposition time in terms of uniform deposition was determined to be 45 min. Different amounts of optimized Cu coated CNT (CNT (Cu)) and Al powders were ball milled. CNT (Cu) reinforced Al (Al-CNT (Cu)) composites were prepared by spark plasma sintering (SPS). Pure CNT reinforced Al (Al-CNT) composites were also prepared by SPS. The ball milled powders and composites were characterized using X-Ray diffraction, scanning electron microscopy, Raman spectroscopy, and transmission electron microscopy (TEM). Microhardness and compression properties of the composites were measured. TEM images of ball milled powders and composites revealed uniform distribution of CNT in matrix. Mechanical properties of Al-CNT (Cu) composites are superior to Al-CNT composites. The maximum enhancement in compressive strength of Al-CNT (Cu) composites is 154% for 2 wt% reinforcement; this enhancement is attributed to the copper coating on CNT surface.

47 citations


Journal ArticleDOI
TL;DR: In this article, the effect of strain rate and nitrogen content on cyclic deformation and substructural changes in 316LN stainless steel was investigated at temperatures 773, 823 and 873 K.

44 citations


Journal ArticleDOI
TL;DR: In this paper, Nitrogen content in 316LN stainless steel with varying nitrogen content (0.07, 0.14 and 0.22) was studied over a range of strain rates at temperatures 773 K, 823 K and 873 K.

37 citations


Journal ArticleDOI
TL;DR: In this paper, Nitrogen and dynamic strain aging induced slip localization in the form of planar slip bands both in IP and OP-TMF, in comparison to IF deformation.
Abstract: Thermomechanical (TMF) and isothermal (IF) fatigue behavior of 316LN stainless steel alloyed with 0.07, 0.14, and 0.22 wt pct nitrogen is presented in this manuscript. In the TMF tests with temperature cycling in the range of 573 K to 873 K (300 °C to 600 °C), life decreased with increasing nitrogen content for both in-phase (IP) and out-of-phase (OP) cycling, with a peak at 0.07 wt pct N. In contrast, 0.14 wt pct N yielded maximum life under IF cycling carried out at 873 K (600 °C). Cyclic lives are seen to follow the sequence, IP-TMF < IF < OP-TMF cycling, and it remained same irrespective of the nitrogen content in 316LN SS. Lives under IP-TMF are lower than those in OP cycling by a factor of 2 to 2.5, in spite of the higher cyclic stress response in OP cycling. At all the nitrogen contents in the present study, nitrogen and dynamic strain aging induced slip localization in the form of planar slip bands both in IP and OP-TMF, in comparison to IF deformation wherein complete planar slip mode of deformation is evidenced only at 0.22 wt pct N. In TMF studies, increasing nitrogen content promoted strong slip localization (i.e., increase in slip band density with a decrease in interband spacing) in combination with high tensile cyclic stresses that marred the beneficial effect of nitrogen content on TMF life.

30 citations


Journal ArticleDOI
TL;DR: In this article, the effect of cutting parameters such as cutting speed, feed, and depth of cut on cutting force, feed force, and radial force was studied. And the analysis of variance (ANOVA) for all the three forces shows that feed rate and depth-of-cut are the significant parameters at 95 % confidence level.
Abstract: The ferrite-bainite-martensite (FBM) multiphase V-microalloyed steel with a yield strength of 1384 MPa was subjected to turning test in order to study the effect of cutting parameters such as cutting speed, feed, and depth of cut on cutting force, feed force, and radial force. The cutting forces are found to decrease with increase in the cutting speed for various feed with constant depth of cut. The analysis of variance (ANOVA) for all the three forces shows that feed rate and depth of cut are the significant parameters at 95 % confidence level, and also, the interaction between cutting parameters is insignificant. The optimum parameter for machining multiphase (FBM) microalloyed steel is found to be cutting velocity 80 m/min, feed rate 0.05 mm/rev, depth of cut 0.1 mm. The multiphase microalloyed steel requires less force as compared to quenched and tempered, microalloyed, and other existing high strength low alloy (HSLA) steels like AISI 4340. The easy machinability of multiphase microalloyed steel is promoted by soft polygonal ferrite (PF) and bainite phases present in the microstructure of the steel.

10 citations


Journal ArticleDOI
TL;DR: Martensite-ferrite microstructures were produced in four microalloyed steels A (Fe-0.44C-Cr-V), B (Fe -0.26C-cr-V) and C (Fe −0.23C-c-v) by intercritical annealing, and the work hardening behavior of these steels at ambient temperature was evaluated through modified Jaoul-Crussard analysis.
Abstract: Martensite-ferrite microstructures were produced in four microalloyed steels A (Fe-0.44C-Cr-V), B (Fe-0.26C-Cr-V), C (Fe-0.34C-Cr-Ti-V), and D (Fe-0.23C-Cr-V) by intercritical annealing. SEM analysis reveals that steels A and C contained higher martensite fraction and finer ferrite when compared to steels B and D which contained coarser ferrite grains and lower martensite fraction. A network of martensite phase surrounding the ferrite grains was found in all the steels. Crystallographic texture was very weak in these steels as indicated by EBSD analysis. The steels contained negligible volume fraction of retained austenite (approx. 3-6%). TEM analysis revealed the presence of twinned and lath martensite in these steels along with ferrite. Precipitates (carbides and nitrides) of Ti and V of various shapes with few nanometers size were found, particularly in the microstructures of steel B. Work hardening behavior of these steels at ambient temperature was evaluated through modified Jaoul-Crussard analysis, and it was characterized by two stages due to presence of martensite and ferrite phases in their microstructure. Steel A displayed large work hardening among other steel compositions. Work hardening behavior of the steels at a warm working temperature of 540 A degrees C was characterized by a single stage due to the decomposition of martensite into ferrite and carbides at this temperature as indicated by SEM images of the steels after warm deformation.

6 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated the precipitation behavior of Al-7Si-0.3Mg/TiB2 composites using differential scanning calorimetry and transmission electron microscopy, and found that Si precipitation is accelerated with increase in TiB2 content.
Abstract: Precipitation behavior of the Al-7Si-0.3Mg/TiB2in situ composites was investigated using differential scanning calorimetry and transmission electron microscopy, and it was found that Si precipitation is accelerated with increase in TiB2 content. Non-isothermal kinetic analysis clearly showed a decrease in the precipitation kinetics of the overaged metastable precipitates in the Mg2Si precipitation sequence.

5 citations


Journal ArticleDOI
01 Aug 2015
TL;DR: In this paper, the influence of process parameters such as cutting speed, feed and depth of cut on surface roughness on both materials was compared and the results showed that the multiphase microalloyed steel exhibited high surface finish than air-cooled steel.
Abstract: Multiphase ferrite–bainite–martensite microalloyed steel produced through a two-step cooling followed by annealing route and a ferrite–pearlite steel obtained through air-cooling after forging were subjected to turning operation. The influence of process parameters such as cutting speed, feed and depth of cut on surface roughness on both materials was compared. The results show that the multiphase microalloyed steel exhibited high surface finish than air-cooled steel. The analysis of variance shows that the contribution of cutting speed and depth of cut on surface roughness are insignificant for both ferrite–bainite–martensite and ferrite–pearlite microstructures.

2 citations