Microstructural and Mechanical Characteristics of in-situ Titanium Metal Matrix Composites
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ISSN : 2319 – 3182, Volume-2, Issue-4, 2013 12 Microstructural and Mechanical Characteristics of in-situ Titanium Metal Matrix Composites K. Srinivasa Vadayar 1 , S. Devaki Rani 2 & V.V. Bhanu Prasad 3 1&2 Dept. of Met. Engineering, JNTUH, College of Engineering, Kukatpally, Hyderabad-85. 3 Scientist „G‟, CCG, DMRL, Kanchanbagh, Hyderabad-58 E-mail : [email protected], Abstract – Discontinuously reinforced titanium matrix composites (DRTMCs) are emerging as an alternate to titanium and its alloys for ambient and elevated temperature applications. The present investigation deals with P/M processing of DRTMCs and their characterization. Ti & B 4 C (1200#, d 50 ≈ 3μm ) powders in three different proportions were blended, compacted and pressureless sintered resulting in Ti matrix composites with 10, 20 &30 vol.% of TiB-TiC reinforcements. Completion of reaction between Ti and B 4 C resulting in Ti, TiB and TiC was confirmed through XRD and microstructural study by SEM. Density, flexural strength, hardness and elastic modulus were measured. TMCs exhibited better mechanical properties in comparison to unreinforced titanium. Key words : Elastic Modulus, Flexural strength, Titanium matrix composites, SEM. I. INTRODUCTION Discontinuously reinforced titanium matrix composites (DRTMCs) are of considerable interest for structural, thermal and armour applications due to the potential for making composites with high specific modulus and strength at relatively low costs. Ranganath et al. [1] produced Ti-TiB-TiC composites by combustion assisted synthesis of Ti-B 4 C (CAS) using arc melting technique. This process could not be followed for synthesizing composites having higher volume fractions of reinforcements due to non uniformity in microstructures. Panda et al. and Sahay et al. [2,3] studied a series of TMCs, with varying volume fractions (30% to 90%) of TiB needles, made by hot pressing the Ti-TiB 2 powders. It was reported that morphology of TiB needle changes depending upon the reinforcement volume fraction in the composite. Bhat et al. [4] produced in-situ TMCs containing high volume fractions of TiB, TiB-TiC, by hot pressing the Ti-TiB 2 and Ti-B 4 C powders, respectively. Their study reported formation of TiB needles in former case while TiB particles in the latter case. Ma et al. [5] prepared Ti-TiB composites with low volume fractions (<15%) of reinforcements by reaction hot pressing the Ti-B, Ti- TiB 2 , Ti-B 4 C and Ti-BN. The hot pressing route followed by the above researchers is expensive and has size & shape limitations. The present investigation is aimed at evaluation of pressureless sintering process to synthesize Ti-TiB-TiC composites out of Ti-B 4 C cold pressed compacts and to study the effect of vol.% of the reinforcement on the microstructural features as well as on the mechanical properties. II. EXPERIMENTAL PROCEDURE Ti-TiB-TiC composites have been synthesized by pressureless reaction sintering of Ti-B 4 C green compacts making use of the following reaction. 5 Ti + B 4 C → 4 TiB + TiC ΔH 298 = -754.36 kJ/mol … (1) Excess titanium over and above the stoichiometric titanium content determined by Eq (1) was used to get necessary amount of matrix titanium. Powders of titanium and three different vol.% of B 4 C (1.8, 3.6 and 5.4 ) have been used to synthesize 10, 20 and 30 vol.% (TiB + TiC) reinforcements, respectively in titanium matrix. Titanium powder made by hydride- dehydrade route having average particle size of 13μm was blended with B 4 C powder having average particle size of 3μm in a roller mill using a poly propylene bottle for 24 hrs. The blended powder was cold compacted into 70 mm x 35 mm x 6 mm compacts at a pressure of 60 MPa for 30 seconds. The green compacts so obtained were subjected to pressureless sintering under 2x10 -3 m.bar vacuum at a temperature of 1450°C for a period of 1 hr. Sintering resulted in integral compacts having ~98.5% theoretical density which are free from cracks and warpage. Shrinkage of 16-18% has been observed in the
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Microstructural and Mechanical Characteristics of in-situ Titanium Metal Matrix CompositesMaterials, Mechanical engineering
Transcript of Microstructural and Mechanical Characteristics of in-situ Titanium Metal Matrix Composites
ISSN :2319 3182, Volume-2, Issue-4, 2013 12 Microstructural and Mechanical Characteristics ofin-situ Titanium Metal Matrix Composites K. Srinivasa Vadayar1, S. Devaki Rani2 & V.V. Bhanu Prasad3 1&2 Dept. of Met. Engineering, JNTUH, College of Engineering, Kukatpally, Hyderabad-85. 3Scientist G, CCG, DMRL, Kanchanbagh, Hyderabad-58 E-mail : [email protected], AbstractDiscontinuouslyreinforcedtitaniummatrix composites(DRTMCs)areemergingasanalternateto titaniumanditsalloysforambientandelevated temperatureapplications.Thepresentinvestigationdeals withP/MprocessingofDRTMCsandtheir characterization. Ti & B4C (1200#, d50 3m ) powders in threedifferentproportionswereblended,compactedand pressurelesssinteredresultinginTimatrixcomposites with10,20&30vol.%ofTiB-TiCreinforcements. Completion of reaction between Ti and B4C resulting in Ti, TiBandTiCwasconfirmedthroughXRDand microstructural study by SEM.Density, flexural strength, hardnessandelasticmodulusweremeasured.TMCs exhibitedbettermechanicalpropertiesincomparisonto unreinforced titanium. Keywords:ElasticModulus,Flexuralstrength,Titanium matrix composites, SEM. I.INTRODUCTION Discontinuouslyreinforcedtitaniummatrix composites(DRTMCs)areofconsiderableinterestfor structural,thermalandarmourapplicationsduetothe potentialformakingcompositeswithhighspecific modulus and strength at relatively low costs. Ranganath etal.[1]producedTi-TiB-TiCcompositesby combustionassistedsynthesisofTi-B4C(CAS)using arcmeltingtechnique.Thisprocesscouldnotbe followedforsynthesizingcompositeshavinghigher volumefractionsofreinforcementsduetonon uniformity in microstructures. Panda et al. and Sahay et al. [2,3] studied a series of TMCs, with varying volume fractions(30%to90%)ofTiBneedles,madebyhot pressingtheTi-TiB2powders.Itwasreportedthat morphology of TiB needlechanges depending upon the reinforcement volume fraction in the composite. Bhat et al.[4]producedin-situTMCscontaininghighvolume fractionsofTiB,TiB-TiC,byhotpressingtheTi-TiB2 andTi-B4Cpowders,respectively.Theirstudyreported formationofTiBneedlesinformercasewhileTiB particles in the latter case. Ma et al. [5] prepared Ti-TiB compositeswithlowvolumefractions(
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