Microstructural and Diffusion Analysis of Au-Sn Diffusion Couple Layer Undergoing Heat Treatment at Near Eutectic Temperatures

Diffusion couples of pure gold and pure tin were created by mechanical cold rolling method. The couples were isothermally treated at temperatures slightly above and below the eutectic temperature near tin-rich region of the equilibrium phase diagram. Differences in the diffusion behaviors were observed as a function of treatment temperatures below (473 K) and above (498 K) the eutectic temperature. At the boundary, it was found that first solid state inter-diffusion was initiated which resulted in local compositional change and solid-state formation of intermetallic compounds. As the composition shifts away towards mixing, the growth of the intermetallic phases was monitored as a function of temperature and time. At temperature above the eutectic, there may be a liquid fraction as the interface isothermally melted. The kinetic involves dissolution of Au atoms into locallized tin-rich liquid. At below eutectic temperature, the formation and growth kinetic of phases follows a solid state diffusion mechanism. By investigation the exponent n values in the growth equation l = k(t/t0)n, the values were found to be in between 0.62 - 0.77 which implies that the kinetics of IMC formations experiment are controlled by both diffusion and intermetallic reaction. The bonding temperature was found to be faster and more reliable at bonding temperature slightly above the eutectic

Study of Microstructure and Mechanical Properties of Commercially Pure Sn and Sn-4%Bi Alloys Fabricated by Permanent Mold Gravity Casting and Forging

The influences of 4 wt% bismuth addition and room temperature strain on microstructure and mechanical properties in tin alloys were investigated in this study. Commercially pure tin and Sn-4%Bi alloys were fabricated by permanent mold gravity casting. The samples were then subjected to forging process at room temperature. As-cast microstructures were compared with 0.25 and 0.5 strained samples. Differential Scanning Calorimetry (DSC) was used to confirm the effect of bismuth on undercooling. The recrystallization and grain growth processes were confirmed by grain size distribution and misorientation study using Electron Backscattered Diffraction (EBSD). Furthermore, position and morphology of the bismuth precipitates were investigated by using Field Emission Scanning Electron Microscope (FESEM). X-ray Photoelectron Spectroscopy (XPS) revealed that tin oxide was the main species found on the surface of these alloys. There was no evidence of bismuth oxide on the surface. Furthermore, the Hall-Petch hardness approximation analysis revealed that there were other influences, which increased the hardness beyond the grain refinement effect

In situ synchrotron characterisation of Fe-rich intermetallic formation during the Solidification of Al-Si-Cu-Fe alloys

The enrichment of Fe during aluminium recycling increases the quantity of Fe-rich intermetallics formed, particularly ß-Al5FeSi, limiting the usage of recycled Al in many fatigue-sensitive applications. In this study, fast synchrotron x-ray tomography was used to investigate microstructure evolution and defect formation in a commercial A319 alloy (Al-7.5Si-3.5Cu, wt.%) with differing Fe-levels (0.2-0.6 wt.%Fe) during in situ solidification and isothermal uniaxial tensile deformation. The captured dynamic changes were quantified using novel image analysis techniques and analysed using computational fluid dynamics. Together these provide new insights into the mechanisms of intermetallic nucleation and growth, and their influence on flow blockage and defect formation. First, time-resolved qualitative and quantitative characterisation revealed that plate-like ß-intermetallics nucleate both off the primary aluminium dendrites in the bulk of the specimen as well as off the oxide skin on the specimen surface. Second, ß-intermetallic formation is largely complete before the formation of the Al-Si eutectic. Third, ß-intermetallics are geometrically complex, demonstrating fast lateral growth and an ability to grow around and in between the primary dendrite arms. Last, direct impingement and potential branching are observed at a wide range of contact angles, indicating that the growth interaction might not be crystallographically related. The presence of ß-intermetallics contributes to several factors that influence defect formation. They block interdendritic flow, increase pore tortuosity and reduce permeability. Pores were observed to grow preferentially along the solid surface of intermetallics, suggesting that ß-intermetallics may reduce the gas-solid interfacial energy and thus facilitate the pore growth. However, they do not nucleate the porosity. The results also show that failure under mild uniaxial semi-solid tension, simulating hot-tearing, displays a much more brittle-like failure mechanism when large ß-intermetallics are present, compared to the more ductile behaviour of the base alloy with unresolved ß-intermetallics.Open Acces

Radial head replacement with the 3D-printed patient-specific titanium prosthesis: Preliminary results of a multi-centric prospective study

Purpose To report preliminary clinical results and safety of 3D-printed patient-specific titanium radial head (RH) prosthesis in treatment of the irreparable RH fractures. Material and methods This multi-centric prospective study included 10 patients (6 men and four women, mean age 41 years (range, 25–64 years)). Three cases were classified as Mason type III and 7 cases as type IV. Patients were assessed preoperatively, intraoperatively, and at 1, 6, 12, 24, 36, and 48 weeks postoperatively. Range of motion (ROM), visual analog scale (VAS) score, Disabilities of the Arm, Shoulder and Hand (DASH) score, Mayo Elbow Performance Score (MEPS), radiology imaging, and laboratory blood and urine testing were evaluated. Results The prostheses were implanted utilizing cemented stems in 5 patients and cementless stems in 5 patients. Intraoperatively, well congruency of a prosthesis with capitellum and radial notch of ulna was observed in all cases. All patients had improvement of ROM, VAS score, DASH score, and MEPS during the postoperative follow-ups. At the final follow-up, mean elbow extension was 6.5° (range, 0°–30°), flexion 145° (range, 125°–150°), supination 79° (range, 70°–80°), and pronation 73.5° (range, 45°–80°). Mean VAS score was 0.3 (range, 0–3), DASH score was 12.35 (range, 1.7–23.3), and MEPS was 99.5 (range, 95–100). Postoperative radiographs demonstrated heterotopic ossification in 2 cases, periprosthetic radiolucency in 2 cases, and proximal radial neck resorption in 2 cases. No one had the evidence of capitellar erosion, implant failure, malpositioning, overstuffing, or symptomatic stem loosening. There was no significant alteration of laboratory results or adverse events related to the 3D-printed prosthesis implantation. Conclusion The preliminary results demonstrated that implantation of the 3D-printed patient-specific titanium RH prosthesis is safe and may be a potential treatment option for irreparable RH fracture

A Patient-Matched Entire First Metacarpal Prosthesis in Treatment of Giant Cell Tumor of Bone

Giant cell tumor of the bones occurring in the first metacarpals frequently requires entire metacarpal resection due to the aggressive nature and high rate of recurrence. Bone reconstruction can be performed with autogenous bone grafts. Here we describe a new technique of reconstruction using a patient-matched three-dimensional printed titanium first metacarpal prosthesis. This prosthesis has a special design for ligament reconstruction in the proximal and distal portions. Good hand function and aesthetic appearance were maintained at a 24-month follow-up visit. This reconstructive technique can avoid donor-site complications and spare the autogenous bone grafts for revision options

The Patient-Specific Implant Created with 3D Printing Technology in Treatment of the Irreparable Radial Head in Chronic Persistent Elbow Instability

Successful treatment of the chronic persistent elbow instability is a challenge for orthopedic surgeons. In this form, it is important to recognize and restore the osseous stabilizer in order to obtain the concentric reduction. In the present report, we describe a case of such injury with irreparable radial head treated with patient-specific radial head prosthesis which was created with 3D printing technology. To our knowledge, this is the first report in clinical use of this kind of prosthesis for the radial head fracture. At a 24-month follow-up visit, the patient was satisfied with the functional outcomes. The Mayo Elbow Performance Index (MEPI) increased from 20 points at the preoperative day to 85 points, and the patient-based Disabilities of the Arm, Shoulder, and Hand (DASH) was reduced from 88.33 points to 28.33 points. Due to the favorable result, replacement of the radial head with the patient-specific implant could be a useful treatment for the irreparable radial head in chronic persistent elbow instability

Understanding the Stress Distribution on Anatomic Customized Root-Analog Dental Implant at Bone-Implant Interface for Different Bone Densities

The aim of this study is to assess the stress distribution on the bone tissue and bone-implant interface of a customized anatomic root-analog dental implant (RAI) by means of finite element analysis (FEA) for different types of bone density. A mandibular right second premolar was selected from the CBCT database. A DICOM file was converted to an STL file to create a CAD model in FEA software. The bone boundary model was created, while bone density types I–IV were determined. Von Mises stress was measured at bone tissues and bone-implant interfaces. To validate the models, the RAI was 3D printed through a laser powder-bed fusion (L-PBF) approach. The results revealed that all RAI designs could not cause plastic deformation or fracture resulting in lower stress than the ultimate tensile stress of natural bone and implant. Compared to a conventional screw-type implant, RAIs possess a more favorable stress distribution pattern around the bone tissue and the bone-implant interface. The presence of a porous structure was found to reduce the stress at cancellous bone in type IV bone density