The effect of thermomechanical welding on the microstructure and mechanical properties of S700MC steel welds.

Grain refinement by plastic deformation during conventional TIG welding can help to compensate for the loss of mechanical properties of welded joints. The thermomechanical welding (TMW) tests were performed on S700MC steel with different combinations of TIG arc energy and high frequency hammering over three target cooling times (t8/5 = 5s, 15s, and 25s). Additionally, the effect of initial microstructures on the weld joint quality was analysed by testing three materials conditions: hot-rolled (as-received) and cold-rolled with 10% and 30% thickness reductions, respectively. The effects of plastic deformation and the mechanical vibration on the grain refinement were studied separately. Optical microscopy, electron backscattered diffraction, and Vickers hardness were used to characterise the weld microstructure heterogeneity. The weld width and depth and the mean grain size were correlated as the function of cooling time t8/5. The results show that the weld dimensions increase with increasing the t8/5. The weld microstructures transformed from the mixed martensite and bainite into mixed ferrite and bainite with increasing the t8/5 time, and the related mean grain size increased gradually. The TMW welds exhibit smaller grains compared to TIG welds due to the coupled effects of mechanical vibration and plastic deformation. The mechanical vibration contributes to weld metal homogenisation, accelerating TiN precipitation in the fusion zone. The proposed TMW process can refine the weld microstructure of S700MC steel, enhancing its mechanical properties.

Electrochemical and Structural Property of TiSiNb TFSOC on Affordable Interconnects in Proton Exchange Membrane Fuel Cell Applications.

High cost and low electrochemical stability of the interconnection in Proton Exchange Membrane Fuel Cell (PEMFC) in the presence of H2SO4 are one of the main issues hindering the commercialization of these devices. This manuscript presents the utilization of cost-effective steel in an attempt to minimize the PEMFC interconnection costs with a thin-film solid oxide coating (TFSOC) providing sufficient corrosion resistance for efficient long-term operation. Novel Ti0.50-y/2Si0.50-y/2Nby1,2O2 as TFSOC was deposited on the C45E steel as a metal interconnect utilizing a sol-gel process at various annealing temperatures. The analysis of the phase and surface morphology demonstrates that lower annealing temperatures developed nanometric crystallite size of 68 nm, more uniform structure and higher corrosion resistance. Under standard test conditions, the TFSOC demonstrated high polarization resistance (1.3 kΩ cm2) even after 720 hours (h). Electrical conductivity of the TFSOC as low as 1.4 × 10-2 (Ω m)-1 and activation energy of 0.20 eV were achieved, which helps to maintain the PEMFC output power.

Performance test of different 3.5 mm drill bits and consequences for orthopaedic surgery.

INTRODUCTION: Drilling of bones in orthopaedic and trauma surgery is a common procedure. There are yet no recommendations about which drill bits/coating should be preferred and when to change a used drill bit. MATERIALS AND METHODS: In preliminary studies typical "drilling patterns" of surgeons concerning used spindle speed and feeding force were recorded. Different feeding forces were tested and abrasion was analysed using magnification and a scanning electron microscope (SEM). Acquired data were used for programming a friction stir welding machine (FSWM). Four drill bits (a default AISI 440A, a HSS, an AISI 440B and a Zirconium-oxide drill bit) were analysed for abrasive wear after 20/40/60 machine-guided and hand-driven drilled holes. Additionally different drill coatings [diamond-like carbon/grafitic (DLC), titanium nitride/carbide (Ti-N)] were tested. RESULTS: The mean applied feeding force by surgeons was 45 ± 15.6 Newton (N). HSS bits were still usable after 51 drill holes. Both coated AISI 440A bits showed considerable breakouts of the main cutting edge after 20 hand-driven drilled holes. The coated HSS bit showed very low abrasive wear. The non-coated AISI 440B bit had a similar durability to the HSS bits. The ZrO2 dental drill bit excelled its competitors (no considerable abrasive wear at >100 holes). CONCLUSIONS: If the default AISI 440A drill bit cannot be checked by 20-30× magnification after surgery, it should be replaced after 20 hand-driven drilled holes. Low price coated HSS bits could be a powerful alternative.