Effect of Direct Aging on Corrosion Behavior of AlSi10Mg Alloy Fabricated by Laser Powder Bed Fusion

Effect of direct aging of 170℃on corrosion behavior of laser powder bed fused AlSi10Mg(LPBF-AlSi10Mg)was studied by microstructure analysis,electrochemical analysis and X-ray photoelectron spectrometer.The results show that direct aging of 170℃has little effect on melt pool and Si cellular structure,but promotes the precipitation of nano-Si particles and releases the residual stress.With increasing aging time from 0 to 4 h to 24 h,the corrosion property of the LPBF-AlSi10Mg is deteriorated,which is evidenced by increased corrosion current density and decreased pitting potential and polarization resistance.With increasing the aging time,the thickness of the oxide film formed on surface of the LPBF-AlSi10Mg increases.The Si content of the oxide film of the sample aging for 4 h is the lowest,9.42 at.%,and it is the highest,18.62 at.%,for the sample aging for 24 h.The electrochemical noise analysis reveals that the middle-frequency contribution of the Hilbert spectrum is responsible for the deteriorated corrosion performance,which corresponds to metastable pitting initiated by nano-Si particles.

Effects of direct aging treatment on microstructure,mechanical properties and residual stress of selective laser melted AlSi10Mg alloy

Direct aging treatment is an important post-processing procedure,yet little research has been done on how it balances the mechanical properties and the stress removal for selective laser melted(SLMed)AlSi10Mg alloys.Here,we proposed a typical direct aging treatment on SLMed AlSi10Mg alloys,and studied the effects on their microstructure,properties and residual stress evolution.The results indi-cate that the as-built microstructure is mainly composed of fine cellularα-Al and reticulated Si phases,and some pre-existing precipitates and dislocations are found in these cells.The direct aging treatment promotes the precipitation of nano-scaled Si phases and preserves a network-like Si structure.Therefore,the strength of the peak-aged alloy increases while the ductility decreases.As the aging temperature in-creases from 160 to 200℃,aging hardening behavior was accelerated significantly.Aging at 160℃ for 4-9 h removes 32.0%-43.0%of the residual stress,which is attributed to the decomposition of the su-persaturatedα-Al matrix,the precipitation of the nano-Si phase and the exposure of low-angle grain boundaries(LAGBs).Considering the overal alloy performance obtained,over-aging at 160℃ for 4 h is the optimized heat treatment regime.Under this condition,the yield strength(YS),ultimate tensile strength(UTS)and elongation(EL)of the alloy in the transverse and longitudinal direction are 309.5 MPa,464.4 MPa and 8.3%and 286.4 MPa,464.9 MPa and 5.1%,respectively.

Safety of direct acting antiviral treatment for hepatitis C in oncologic setting:A clinical experience and a literature review

With a globally estimated 58 million people affected by,chronic hepatitis C virus(HCV)infection still represents a hard challenge for scientific community.A chronic course can occur among patients with a weak innate ad adaptive response with cirrhosis and malignancies as main consequences.Oncologic patients undergoing chemotherapy represent a special immunocompromised population predisposed to HCV reactivation(HCVr)with undesirable changes in cancer treatment and outcome.Aim of the study highlight the possibility of HCVr in oncologic population eligible to chemotherapy and its threatening consequences on cancer treatment;underline the importance of HCV screening before oncologic therapy and the utility of direct aging antivirals(DAAs).A comprehensive overview of scientific literature has been made.Terms searched in PubMed were:“HCV reactivation in oncologic setting”“HCV screening”,“second generation DAAs”.Pharmacokinetic and Pharmacodynamics characteristics of DAAs are reported,along with drug-drug interactions among chemotherapeutic drug classes regimens and DAAs.Clinical trials conducted among oncologic adults with HCV infection eligible to both chemotherapy and DAAs were analyzed.Viral eradication with DAAs in oncologic patients affected by HCV infection is safe and helps liver recovery,allowing the initiation of cancer treatment no compromising its course and success.

Effect of Direct Ageing Treatment on Stress-Rupture Properties of GH761 Alloy

The effect of direct ageing treatment on microstructure and stress-rupture properties of GH761 alloy was studied. Phosphorus was added to the tested alloy for its beneficial effect on stress-rupture life. It was found that the grain size of the tested alloy became much finer after direct ageing treatment, in comparison with the commercial GH761 alloy under standard heat treatment condition. The optimum direct ageing treatment has been determined as follows： 830 ℃ × 4 h, air cooling＋ 720 ℃ × 24 h, air cooling. After such treatment, the higher stress-rupture prop- erties of the test alloy at 650 ℃, 690 MPa were obtained. The role of phosphorus is still effective under the condition of direct ageing treatment.

Precipitation Behaviour at the Interface of an Additively Manufactured M789-N709 Hybrid Alloy

A novel hybrid alloy, designed for plastic injection dies, was fabricated by depositing M789 steel on wrought N709 steel through laser powder bed fusion (LPBF). The M789-N709 interface (with a thickness of about 300 μm) is characterized by the variation of titanium content from 0 wt% in the N709 section to about 1 wt% near the M789 region. A thermodynamic and kinetic simulation after aging treatment was performed to reveal the precipitation behavior in the M789-N709 interface. Different sizes and amounts of ETA-Ni3(Ti,Al) strengthening precipitates exist, with a maximum volume fraction and radius of about 5% and 5 nm, respectively (near the M789 region). Moreover, the volume fraction of precipitates significantly increases with Ti additions of up to 0.6 wt% (i.e., 100 μm from the N709 region);however, beyond this threshold, the increase in the amount of precipitation becomes gradual. The thermodynamic and kinetic simulations performed in the interface are validated by electron diffraction spectroscopy (EDS), electron probe microanalyzer (EPMA) and atomic probe tomography (APT) results;the measured precipitate size from the APT analysis is consistent with the simulation results. Two morphologies of precipitates were detected: elongated and spherical;both contribute to the robustness of the interface. The robust M789-N709 interface formed during the process shows good compatibility between the alloys, which is critical for extended tool life. These new insights about the precipitation at the interface of M789-N709 alloy are crucial in assessing the feasibility of N709 as a cost-effective base material to minimize the use of M789 when printing plastic injection dies.