A Study of Tensile Deformation, Fracture Characteristics and Beta Brittleness in Alpha-beta Titanium Alloy PDF Download

Author: Kaiyan Jiang
Publisher:
ISBN:
Category :
Languages : en
Pages : 8

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Author: Udaykar Bathini
Publisher:
ISBN:
Category : Civil engineering
Languages : en
Pages : 131

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Rapid industrial growth and advances in the domains of engineering and related technologies during the last fifty years have led to the extensive use of traditional metals and their alloy counterparts. Titanium is one such metal which has gained wide popularity in the aerospace and defense related applications owing to a wide range of impressive mechanical properties like excellent specific strength ([sigma]UTS/[rho]), stiffness, corrosion and erosion resistance, fracture toughness and capability to withstand significant temperature variations. Two materials, namely commercial purity titanium (Grade 2), referred to henceforth as Ti-CP (Grade 2) and the "work-horse" alloy Ti-6Al-4V have been chosen for this research study. The intrinsic influence of material composition and test specimen orientation on the tensile and fatigue behavior for both Ti-CP (Grade 2) and Ti-6Al-4V have been discussed. Samples of both Ti-CP (Grade 2) and Ti-6Al-4V were prepared from the as-provided plate stock along both the longitudinal and transverse orientations. The specimens were then deformed to failure in uniaxial tension for the tensile tests and cyclically deformed at different values of maximum stress at constant load ratio of 0.1 for the high cycle fatigue tests. The microstructure, tensile properties, resultant fracture behavior of the two materials is presented in the light of results obtained from the uniaxial tensile tests. The conjoint influence of intrinsic microstructural features, nature of loading and specimen properties on the tensile properties is discussed. Also, the macroscopic fracture mode, the intrinsic features on the fatigue fracture surface and the role of applied stress-microstructural feature interactions in governing failure for the cyclic fatigue properties for both the materials under study Ti-CP (Grade 2) and the "work-horse" alloy Ti-6Al-4V have been discussed in detail. Careful study of the microstructure for Ti-CP (Grade 2) material at a low magnification revealed the primary alpha grains to be intermingled with small pockets of beta grains. Observation at the higher allowable magnifications of the optical microscope revealed very fine alpha phase lamellae located within the beta grain. The microhardness and macrohardness measurements were consistent through the sheet specimen for Ti-CP (Grade 2) and slightly lower compared to Ti-6Al-4V. However, the macrohardness was marginally higher than the microhardness resulting from the presence of a large volume fraction of the soft alpha phase. The hardness values when plotted reveal marginal spatial variability. Tensile fracture of Ti-CP (Grade 2) was at an inclination to the far field tensile stress axis for both longitudinal and transverse orientations. The overload region revealed a combination of fine microscopic cracks, microscopic voids of varying size and randomly distributed through the surface, and a large population of shallow dimples, features reminiscent of locally brittle and ductile failure mechanisms. The maximum stress ([sigma]maximum) versus fatigue life (Nf) characteristics shown by this material is quite different from those non-ferrous metals that exhibit a well-defined endurance limit. When compared at equal values of maximum stress at a load ratio of 0.1, the fatigue life of the transverse specimen is noticeably greater than the longitudinal counterpart. At equivalent values of maximum elastic strain, the transverse specimens revealed noticeably improved fatigue life as compared one-on-one to the longitudinal counterparts. Careful observations of the Ti-6Al-4V alloy microstructure over a range of magnifications spanning very low to high magnification revealed a duplex microstructure consisting of the near equiaxed alpha and transformed beta phases. The primary near equiaxed shaped alpha grains (light in color) was well distributed in a lamellar matrix with transformed beta (dark in color). The microhardness and macrohardness values recorded for the Ti-6Al-4V alloy reveal it to be harder than the commercially pure (Grade 2) material. However, for the Ti-6Al-4V alloy the microhardness is noticeably higher than the corresponding macrohardness value that can be ascribed to the presence of a population of processing-related artifacts and the hard beta-phase. Tensile fracture of the Ti-6Al-4V alloy was macroscopically rough and essentially normal to the far field stress axis for the longitudinal orientation and cup-and-cone morphology for the transverse orientation. However, microscopically, the surface was rough and covered with a population of macroscopic and fine microscopic cracks, voids of varying size, a population of shallow dimples of varying size and shape, features reminiscent of locally brittle and ductile failure mechanisms. When compared at equal values of maximum stress at a load ratio of 0.1, there is a marginal to no influence of microstructure on high cycle fatigue life of both orientations of the alloy.

Author: Zachary Thomas Kloenne
Publisher:
ISBN:
Category : Microscopy
Languages : en
Pages : 137

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Titanium and its alloys are very important to the advancement of aviation technology, as the strength-to-weight ratio of these alloys make them ideal for increased efficiency. Historically, alpha/beta titanium alloys have been used in the low temperature, low pressure region of a turbine engine, with Ti-6Al-4V being the most commonly used alloy, often referred to as the "workhorse" titanium alloy. However, Ti-6Al-4V experiences limitations in ductility, low-temperature machinability, fracture toughness, and perhaps most importantly, cost. To address these issues, alloy development was performed at TIMET corporation, with a focus on a low-Al containing alloy. A series of alloys were produced, with high strain rate mechanical response serving as a barometer for desired properties. Using this method, the alloy TIMETAL-407, referred to as Ti-407 henceforth, was developed, with an nominal composition of: Ti-0.85Al-3.85V, 0.25Fe-0.25Si-0.15O (wt.%), with the remaining balanced by titanium. Ti-407 displayed remarkable high strain rate properties, lending toward applications requiring increased resistance to impact loading. In addition to improved energy absorption properties, the low alloying content offers cost benefits when compared with its counterpart alloys, namely Ti-6Al-4V and Ti-3Al-2.5V. While enhanced properties in Ti-407 were observed in both high strain rate and nominal strain rate testing, the source of these properties remained unidentified. This work attempted to elucidate the bases for improved mechanical response in Ti-407. This has been achieved through a series of mechanical tests, followed by advanced characterization of deformed specimens. Additional insight was gained through through comparison of deformation mechanisms in Ti-407 with Ti-6Al-4V and Ti-3Al-2.5V, which provided information on opposed mechanisms. The results uncovered in this study have revealed a number of novel mechanisms related to the deformation of Ti-407, which included anomalous c+a dislocation activity in grains oriented favorably for a-type prismatic slip, reduced localization of slip, increased propensity for a-type pyramidal slip, and deformation through sliding at the alpha/beta interfaces. Reduction in slip localization has been attributed to the low Al content of Ti-407, while the source of interface sliding and c+a dislocation activity has been attributed to a segregation of Si to the alpha/beta interface, which results in a distortion to the alpha/beta interface, locally. The distortion has been determined to affect the habit plane of the alpha/beta interface.

Author: G. Zhiming
Publisher:
ISBN:
Category :
Languages : en
Pages : 18

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Author: Daniel Eylon
Publisher: Minerals, Metals, & Materials Society
ISBN:
Category : Titanium alloys
Languages : en
Pages : 556

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Beta titanium alloys are one of the most rapidly developing areas of materials technology. As a group, beta alloys provide a wider range of processing, physical, chemical and mechanical properties than any other titanium alloys.

Author: Mithun Kuruvilla
Publisher:
ISBN:
Category : Mechanical engineering
Languages : en
Pages : 207

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"Titanium, which is referred as a "wonder metal" has been in use for structural application for more than 50 years both in the form of commercially pure titanium and alloys. The wide range of mechanical properties exhibited by titanium led to the development of various alloys tailored for specific application in areas spanning aerospace to sports. The innovatively engineered titanium alloy ATI 425TM is an emerging high performance, high strength alloy and a viable replacement to the work horse and most commercially popular titanium alloy Ti-6Al-4V. This newly emerged alloy offers the inherent advantage of being receptive to mechanical deformation by cold working. Initially this alloy was developed and put forth for use as armor plate for ballistic protection. This alloy also shows promise for use in aerospace-related applications. In this thesis report is presented and discussed the final fracture behavior of the alloy deformed under both quasi static and cyclic fatigue loading conditions, highlighting the role of product form in governing the mechanical deformation and fracture behavior. Samples of the alloy were prepared from both rod stock and sheet stock, and deformed with stress axis both parallel and perpendicular to the longitudinal direction for the sheet stock and along the longitudinal axis for the rod stock. The intrinsic influence of processing on microstructure of the rod revealed alpha grains of varying size and shape being well distributed through the transformed beta matrix. The hardness measurements were consistent and the macrohardness was found to be about half the value of the microhardness. Tensile properties of this alloy are comparable with the commercial alloy Ti-6Al-4V, within the limits of experimental scatter. The tensile deformed fracture surface was macroscopically rough and microscopically, reminiscent of locally ductile and brittle failure mechanisms. The influence of intrinsic microstructural features of the alloy product and nature of loading on final fracture behavior is discussed. The high cycle fatigue resistance of the chosen titanium alloy revealed a trend shown by most non- ferrous metallic materials. The final fracture behavior of the alloy under cyclic loading conditions showed differences in the nature and volume fraction of the features with maximum stress at a given load ratio. The processing on the sheet stock of both orientations resulted in alpha plus beta microstructure. The microhardness and macrohardness data reveals the alloy to be harder in the transverse orientation than in the longitudinal orientation. The tensile properties of the sheet stock with transverse orientation, when compared to the commercial alloy Ti-6Al-4V were observed to be better than sheet stock with longitudinal orientation. The tensile fracture surface of the alloy sheet along the longitudinal orientation revealed at the macroscopic level a fairly rough transgranular region and at microscopic level a healthy population of microscopic voids and shallow dimples of varying size and shape. For the transverse test specimen, the tensile fracture surface was macroscopically rough and globally at an inclination to the far field stress axis and microscopically it was rough and covered with a healthy population of voids of varying and dimples of varying size and shape. The high cycle fatigue resistance of the chosen titanium alloy revealed that the transverse oriented specimens showed more fatigue resistance compared to the longitudinal ones. Cyclic fatigue fracture surfaces revealed differences in the nature and volume fraction of the features with maximum stress at a given load ratio. The region of crack initiation and early crack growth and stable crack growth was essentially flat and transgranular."--Abstract.

Author:
Publisher: ASTM International
ISBN:
Category :
Languages : en
Pages : 304

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Author: Fred J. Gurney
Publisher:
ISBN:
Category : Deformations (Mechanics)
Languages : en
Pages : 92

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The inter-relation of extrusion process variables with mechanical properties and microstructure is analyzed for three titanium alloys (Ti-5Al-2.5Sn, Ti-6Al-4V and Ti-13V-11Cr-3Al). Information is obtained from duplicate billets which were extruded at same conditions with one extruded bar allowed to air cool and the other bar water quenched immediately after extrusion. Results indicate that significant reduction in deformation loads can be achieved in alpha and alpha-beta titanium alloys by processing them in the beta temperature range. Resultant metallurgical structures and mechanical properties (room temperature tensile and Charpy V notch impact) are found to not be significantly affected by process variables other than preheat temperature and product cooling rate. In alpha and alpha-beta alloys, the room temperature strength properties of beta processed and water quenched product is significantly improved over those of beta processed and air cooled product and somewhat improved over those for alpha-beta processed followed by either air cooling or water quenching. Mechanical properties from the beta alloy are not significantly affected by process temperature or by product cooling rate except for some anomalous behavior in the 2050F processing temperature range. (Author).

Author: C. S. Lee
Publisher:
ISBN:
Category :
Languages : en
Pages : 17

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Alpha-beta interfaces play an important role in the mechanical properties of alpha/beta alloys. These interfaces are the sites of hydrogen segregation and hydride precipitation. In addition there have been a number of investigations which have reported the presence of what has been designated interface phase, and the role of the interface phase on transmitting deformation across the interface has been considered in two separate investigations. Numerous observations have been made that voids formed at alpha/beta interfaces. Fatigue cracks have been observed to form and propagate along alpha/beta interfaces. Catastrophic fracture has also been found to occur at these interfaces. All of these observations attest to the importance of alpha/beta interfaces in controlling properties of alpha/beta Ti alloys. Although plastic deformation studies of single crystal alpha-Ti have been carried out and single crystal studies of Beta-Ti have been made, no studies, up to this investigation, have been carried out on alpha/beta bimetallic bicrystals.

Author: D. J. Maykuth
Publisher:
ISBN:
Category : Sheet-metal work
Languages : en
Pages : 164

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