Functionally graded Ni-Ti microstructures synthesised in process by direct laser metal deposition

The fabrication of biomedical devices using Ni-Ti compositions is limited to conventional techniques and the use of near equiatomic pre-alloyed Ni and Ti powders. In this study, functionally graded walls and cylinder built by concurrent feeding of Ni powder and commercially pure (CP) Ti wire using direct laser metal deposition technique are presented. The built structures consist of CP Ti wire-deposited layers and Ni-Ti layers of varying Ni composition. The microstructures of the built Ni-Ti structures including phase identification, phase compositions and area fractions of the phases present at various processing parameters were determined using a combination of scanning electron microscopy/ energy dispersive X-ray spectroscopy, X-ray diffractometry and image processing software. Vickers microhardness test was conducted on the deposited structures. It was found that the Ni-Ti layers comprise of NiTi and NiTi2 phases. The area fraction of the NiTi phase increases, whereas NiTi2 decreases with increasing the Ni powder feed rate. Ni-Ti layers with higher area fractions of NiTi2 phase are found to be harder with a maximum of 513 HV0.3 found in this study. The micro-hardness of Ni-Ti layers is, by at least a factor of 1.5, higher than the CP Ti wire laser-deposited layers

Development of metal matrix composites by direct energy deposition of ‘satellited’ powders

Limited research has been undertaken investigating the material design freedoms that are granted through the use of additive manufacturing methods, especially in the development of materials specifically formulated for additive processes. In this study, a new material combination was evaluated for use with directed energy deposition methods of additive manufacturing. Here, a Ti-6Al-4 V powder is processed in combination with a much finer titanium diboride powder following a satelliting procedure. The resulting combination consists of large Ti-6Al-4 V particles encased in finer titanium diboride. Deposited composites presented exhibit TiB needles associated with increased hardness. Processing conditions were detailed which permit the deposition of the prepared feedstock onto Ti-6Al-4 V substrates. Microstructural characterisation revealed that the composite was made up of eutectic TiB precipitates dispersed in α-β Ti matrix with few partially melted Ti-6Al-4 V and TiB2 particles. Satelliting TiB2 powder onto Ti-6Al-4 V particle surfaces has significantly improved the homogeneity of composite which is characterised with randomly oriented and uniform distribution of TiB needles in the microstructure. Hardness of composites ranged between 440–480 HV. Hence, the feedstock preparation method proposed has been found to be effective and can be adapted for low cost and rapid formulation of a host of materials for processing by additive manufacture

A review of various improvement strategies for joint quality of AA 6061-T6 friction stir weldments

Aluminium alloys are one of the choice materials with ever-increasing demands in manufacturing industries. The aluminium alloy 6 xx series such as AA6061-T6, has emerged as one of the promising materials utilized owing to its combination of favourable properties which include high strength to weight ratio, good ductility, excellent corrosion resistance and relatively low cost. These superior properties are responsible for its emergence and usage in the fabrication of aircraft wings and fuselages, yacht/ship construction, automotive rims and wheel spacers. However, joining of AA6061-T6 including the use of friction stir welding (FSW) has serious concerns because the mechanical and tribological properties of the AA6061-T6 welded joints deteriorate significantly compared with the base metal. This phe�nomenon has been attributed to the severe softening encountered at the stir zone (SZ) of the aluminium matrix during FSW. Other inherent challenges of FSW such as weld thinning, kissing bond and keyhole formation also contribute to the reduction in the weld joint quality. The softening phenomenon has been linked to the dissolution of the strengthening pre�cipitates (B00-Mg5Si6) as a result of high heat input during the welding process. Hence, this paper attempts to review the various improvement strategies adopted in the existing studies to improve the quality of AA 6061-T6 welded joint. These include parametric optimization, selection of appropriate tool design, pre and post heat treatments, adoption of different groove/hole designs for particle addition as well as the addition of reinforcement particles to the weld joint. The variants of FSW recently developed will also be considered. The findings from the review will generally be useful for future work on FSW of heat treated aluminium alloys. The evolution of FSW and its associated challenges are briefly discussed while the research areas yet to be harnessed are suggested for future works

Tensile strength prediction by regression analysis for pulverized glass waste-reinforced aluminium alloy 6061-T6 friction stir weldments

AA6061-T6 is becoming a material of choice in the automobile, marine and aerospace industries because of its combination of relatively favourable and superior properties including high toughness, strength and excellent corrosion resistance. The major issue of concern about this material is the deterioration of these properties in the welded joint which has been established to improve through the additions of synthetic rein�forcements such as SiC, WC, Al2O3, B4C and SiO2. This study seeks to investigate the quality of pulverised glass waste-reinforced friction stir welded joints of AA6061-T6 within a process window (rotational speed: 900-1400 rpm; traverse speed: 25-63 mm/min; tilt angle: 1� - 2.5�) as well as developing a regression model predicting the tensile strength of the pulverised waste glass-reinforced AA6061-T6 friction stir welded joints at varying process parameters. The tensile strength of the weldment was determined using Instron universal testing machine while the model was developed using a new statistical method (analysis of variance and hierarchy rule). The effects of the interaction of the parameters on the joint quality were also determined. Optimum tensile strength of *185 MPa was achieved at rotational speed of 1120 rpm, traverse speed of 40 mm/min and tilt angle of 1.5.There is an improvement of about 37% over the unreinforced joint with tensile strength of *135 MPa. A model with a prediction accuracy of 92% was developed. The analysis of variance revealed that tool rotational speed, traverse speed and tilt angle had significant effects on the tensile strength of the weldments while the factors’ interactions do not show any significant contribution to the tensile strength. The model finds technical applications where timely selection of optimum process parameters is required for producing particulate-reinforced AA6061-T6 friction stir welded joints

Joint quality enhancement of AA6061-T6 friction stir weldment by reinforcing with pulverized glass waste using different reinforcement strategies

The joint quality performance of AA6061-T651 friction stir weldments had been investigated in this study through addition of pulverized waste glass (PWG), palm kernel shell ash (PKSA) and synthetic silicon carbide (SSC) with a bid to enhancing some selected mechanical properties. Optimized processing parameters which include 1120 rpm rotational speed, 40 mm/min traverse speed, 1.5o tilt angle) and optimum reinforcement strategy (parallel hole) established from a preliminary investigation were utilized for the friction stir welding. The mechanical properties such as the tensile strength, hardness and impact energy were then further investigated. The results showed that the mechanical properties of all the reinforced welded joints improved significantly than the unreinforced joint having a relatively reduced joint performance of 132 MPa tensile strength, hardness of 45.3 HRB and impact energy of 39.4 J. The PWG-reinforced friction stir welded joint performed optimally at a tensile strength of 212.7 MPa, 72 HRB hardness and 54.5 J impact energy followed by the SSC-reinforced joint which exhibited 173.7 MPa tensile strength, 54.8 HRB hardness and impact energy of 41.7 J. Hence, 80%, 59% and 38% joint performance was exhibited through tensile strength, hardness and impact energy of PWG-reinforced friction stir weldments of AA6061-T651 against the unreinforced weldments

Mechanical Properties and Microstructural Characterization of Aged Nickel-based Alloy 625 Weld Metal

The aim of this work was to evaluate the different phases formed during solidification and after thermal aging of the as-welded 625 nickel-based alloy, as well as the influence of microstructural changes on the mechanical properties. The experiments addressed aging temperatures of 650 and 950 A degrees C for 10, 100, and 200 hours. The samples were analyzed by electron microscopy, microanalysis, and X-ray diffraction in order to identify the secondary phases. Mechanical tests such as hardness, microhardness, and Charpy-V impact test were performed. Nondestructive ultrasonic inspection was also conducted to correlate the acquired signals with mechanical and microstructural properties. The results show that the alloy under study experienced microstructural changes when aged at 650 A degrees C. The aging was responsible by the dissolution of the Laves phase formed during the solidification and the appearance of gamma aEuro(3) phase within interdendritic region and fine carbides along the solidification grain boundaries. However, when it was aged at 950 A degrees C, the Laves phase was continuously dissolved and the excess Nb caused the precipitation of the delta-phase (Ni3Nb), which was intensified at 10 hours of aging, with subsequent dissolution for longer periods such as 200 hours. Even when subjected to significant microstructural changes, the mechanical properties, especially toughness, were not sensitive to the dissolution and/or precipitation of the secondary phases

A parametric study of Inconel 625 wire laser deposition

AbstractLaser deposition with wire offers saving potentials over powder based systems. These include a cleaner processing environment, reduced economic and environmental cost of producing the wire, better surface finish and higher material deposition rates. This technique is rapidly finding applications for the manufacture and repair of high value components. For the first time, the deposition of Inconel 625 wire for single tracks at varying processing parameters using a 2-kW Ytterbium doped fibre laser has been investigated. A process map predicting the process characteristics in terms of wire dripping, smooth wire transfer and wire stubbing at different cladding conditions has been developed. Track geometrical characteristics including aspect ratio and contact angle were evaluated using surface profilometry and optical microscopy. Scanning electron microscopy equipped with energy dispersive X-ray spectroscopy was used to determine the dilution ratio (%) of the tracks. Wire deposition volume per unit length of track and energy per unit length of track were found to be key parameters influencing both the process and track geometrical characteristics. Aspect ratio and dilution ratio showed positive dependency whereas contact angle showed negative dependency on energy per unit length of track. Conversely, material deposition volume per unit length of track varied directly with contact angle but inversely with aspect ratio and dilution ratio (ranging from 0% to 24%). Processing conditions at which a combination of favourable single track properties including low contact angle (<80°), minimal dilution ratio (5–13%) and high surface quality were achieved are presented. These properties are required for depositing overlapped tracks of good surface finish, minimal dilution and free of inter-run porosity

Influence of cashew steaming on the quality attributes of cashew-pawpaw mixed fruit juice

Cashew is a tree crop that is valued for its nuts, with the fleshy fruits (cashew apple) receiving little attention due to its high acidity. In this study, ascorbic acid, total solid, total soluble solid, pH, titratable acidity and microbial stability of cashew-pawpaw juice prepared by mixing varying proportions (90:10, 80:20, 70:30, 60:40, 50:50) of raw or steamed cashew and pawpaw puree were evaluated. Increased in ascorbic acid (10.20-23.96 mg/100 g), total solid (8.03-12.37%), total soluble solid (1.37-3.5%) and pH (3.68-4.65) were recorded for the cashew-pawpaw juice samples. The titratable acidity (TTA) of the juice samples decreases (0.39-0.19%) with increasing amount of pawpaw puree in the juice blends. Total yeast and total coliform were not detected in the juice samples, however, the juice had low (1 × 105 - 1.5 × 105 log10 cfu/ml) total viable count. Cashew-pawpaw juice blend prepared from 50% raw cashew juice and pawpaw puree was highly rated in terms of taste, colour, flavor and overall acceptance. In conclusion, acceptable low acid juice that is also rich in ascorbic acid can be produced from blend of raw cashew and pawpaw puree. Keywords: Cashew juice; Pawpaw puree; Physicochemical properties; Steamed cashew; Vitamin C