In the present study, investigation and comparison laser and tungsten inert gas (TIG) welding techniques for dissimilar butt joint of 304L and 316L stainless steel sheets was carried out. The effects ...of voltage and laser beam spot size during laser welding and effects of voltage, traveling speed and presence of backing gas during TIG welding on yield strength, elongation, hardness and weld width were investigated. Moreover, in order to examine the mechanical and metallurgical behavior of the weld, microstructure analysis was used. Results showed that welding depth of TIG welding was higher than laser method. It was observed that strength and toughness of samples decreased by increasing voltage in TIG and laser welding. Additionally, by increasing beam spot size in laser welding, strength, toughness and hardness increased. Also, the presence of backing gas during TIG welding resulted in the increase of strength, toughness and hardness of the samples.
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•Enhancement of the strength and toughness because of increase of beam spot size.•Change of temperature gradient resulted in layer microstructure in TIG samples.•TIG samples with backing gas had higher strength and finer isothermal layers.•Massive austenite in laser samples because of massive transformation.
Abstract
This study investigated a suitable filler metal, diffusion depth of the elements of this filler metal in the base metal, and its effect on the mechanical properties of brazing bonding of ...sheets with different thicknesses of 304L stainless steel. For this purpose, brazing was performed with thermal induction under a vacuum of 10
−5
mbar and filler metal BNi-2 at the corner structures. First, the microstructure of different joint regions including base metals, Ni affected areas, and interfaces were examined by scanning electron microscopy and then the relationships between microstructure and microhardness were compared. In sheets with different thicknesses, the differences in diffusion depth were observed. Moreover, the microhardness of different areas of the braze was revealed to be completely affected by the diffusion of nickel. Finally, it was found that, for the bonding between 304L sheets with different thicknesses, BNi-2 filler metal had reasonable strength, diffusion, and filling for vacuum applications.
In this paper, a type of soft metal binder of diamond tools (diamond segments) that was consisted of 78% Brass (Cu-10Zn) +16% Bronze (Cu–10Sn) + %6Co was investigated. The first, it was approved that ...the binder is a soft metal binder by a hardness test for diamond tools in natural stones cutting. Then, the effective factors on grinding efficiency such as specific energy (SE), Cutting force (FC), metal binder removal rate (MRR), grinding ratio (G-ratio), wear resistance and Mean free path (MFP) were evaluated by different formula and equations. On the other hand, the effect of different wear mechanisms on the metal binder and diamond grits of the tool was evaluated by the cutting of a type of very hard marble stone that calls Cappochino Beige Marble (CBM). The existence of wears of abrasive, surface fatigue, impact and erosive were confirmed by scanning electron microscopic observations. According to hardness 73 HRB (hardness of the binder) and the wears, there is a short tools life for the diamond tool due to low wear resistance of the metal binder but, the cutting rate was high.
The rising price of decorative stones will increase the final price of the stones and will overshadow the global market of decorative stones. The presence of cobalt, iron, chromium and nickel powders increases the price of diamond tools because of their high price. On the other hand, due to the higher temperature and time of hot press to produce these tools by the mentioned powders, it will also increase the price. Therefore, in this paper, brass and bronze alloy powders, which are much cheaper than cobalt, iron, chromium and nickel powders, have been used as main metal binder powders to reduce raw material prices and manufacturing process costs. On the other side, due to the creation of a softer metal binder compared with the more expensive and harder binder of cobalt, iron, chromium and nickel powders, it can be affected to increase the cutting speed because of increasing wear of the binder. Therefore, mathematical calculations are essential for the efficiency of the tools' cutting.
•Creating a soft metal binder for diamond tools by Brass/Bronze + low cobalt.•Grinding efficiency calculations of diamond tools by cutting of very hard marble stone.•Existence of wears of abrasive, surface fatigue, impact and erosive in diamond tools for cutting of beige marbles.
In this study, the tribological behavior of PDC-cutter including WC particles/Ta-20Nb binder composite as substrate and polycrystalline diamond composite as PCD layer produced by high pressure-high ...temperature (HPHT) for drilling applications was investigated. To examine the metallurgical behavior, phase analysis, hardness of substrate and PCD layer, and tribological behavior, scanning electron microscopy, X-ray diffraction, Vickers microhardness, and wear tests were used, respectively. Due to the HPHT of the manufacturing process, the high hardness of the interfaces, especially for the WC/Ta-20Nb was achieved, which had ∼28% higher hardness than the diamond grits/Ta-20Nb binder. Therefore, no obvious porosity was observed in the interfaces and the composites were completely densified because the particles had good retention strength. The wear results showed that the tribological behavior of PCD layer/granite or marble pairs was directly influenced by the binder content, with samples having a lower binder content showing superior wear performance. Additionally, worn surface investigations demonstrated that adhesive and abrasive wear mechanisms were present in all pairs, with their intensities being strongly correlated with the binder concentration.
•Creating Ta solid solution at the interfaces prevents forming brittle compounds.•Diffusion of W, Ti, Nb and C in Ta creates high hardness of interfaces.•Compensating for lack of strengthening of interstitial C in PCD layer with a higher CTE.
•The effect of heat treatment on the diffusion layers of laminated composites was investigated.•The formation of solid solution and intermetallic layers at the interfaces of metal strips.•Diffusion ...controlled mechanism for brass and interface controlled mechanism for intermetallic compounds were dominated.•11% difference of the thickness for the calculated diffusion layer with the actual thickness.
In this study, the effect of heat treatment on the laminated Mg/Zn/Cu/Al composite produced by accumulative roll bonding (ARB) was investigated. For this purpose, interfacial microstructural formed during the heat treatment were investigated. The results showed that with increase in both temperature and time, the diffusion layers (DLs) grew. The brass, (Al,Cu), and (Mg,Zn) layers created that is related to the diffusion and interface migration. The growth of the brass layer was diffusion controlled and the growth of the (Al,Cu), and (Mg,Zn) layers were mixed controlled. In both of them, chemical compositions were changed and new phases created as DLs.
It was shown that new high-manganese austenitic steels can be used as an alternative to conventional Ni–Cr austenitic steels especially in vacuum vessels. In this study, a nickel-free austenitic ...steel with chemical composition of 24 wt.% Mn, 10 wt.% Cr, 0.13 wt.% C and trace elements of Si, Ti, V, W, and Al was hot-rolled at 950 and 1100 °C to different strains. Microscopic observations, X-ray diffraction, tensile, impact and microhardness tests were performed to characterize the microstructural aspects and mechanical properties. A small amount of chromium carbide was found on the grain boundaries of this fully austenitic steel. The results showed that the microstructure and mechanical properties of hot rolled manganese austenitic steel are affected by the dynamic recrystallization and twinning phenomena. Also, by changing the grain morphology from equiaxed to elongated, strength and hardness increased, and the impact toughness and ductility were reduced.
What is known and objective
Although antibiotics are ineffective against viral infections, epidemiological studies have revealed that the COVID‐19 pandemic resulted in the overuse of antibiotics and ...disruption of antimicrobial stewardship programmes. We investigated the pattern of antibiotic use during the first 6 months of the COVID‐19 pandemic in Iran.
Methods
A multi‐centre retrospective study was designed to investigate the use of 16 broad‐spectrum antibiotics in 12 medical centres. The rate of antibiotic use was calculated and reported based on the Defined Daily Dose (DDD) per 100 hospital bed‐days. The bacterial co‐infection rate was also reported.
Results and discussion
Totally, 43,791 hospitalized COVID‐19 patients were recruited in this study. It was found that 121.6 DDD of antibiotics were used per 100 hospital bed‐days, which estimated that each patient received approximately 1.21 DDDs of antibiotics every day. However, the bacterial co‐infections were detected only in 14.4% of the cases. A direct correlation was observed between the rate of antibiotic use and mortality (r142 = 0.237, p = 0.004). The rate of antibiotic consumption was not significantly different between the ICU and non‐ICU settings (p = 0.15).
What is new and conclusion
In this study, widespread antibiotic use was detected in the absence of the confirmed bacterial coinfection in COVID‐19 patients. This over‐consumption of broad‐spectrum antibiotics may be associated with increased mortality in hospitalized COVID‐19 patients, which can be an alarming finding.
Detailed consumption rate (ACI) of each antibiotic in 12 included MCs during the first 6 months of COVID‐19 pandemic in Iran. ACI, antibiotic consumption index; DDD per 100 bed‐days.
Background: Fipronil systemic insecticide and integrated vector management (IVM) leading to control and/or reduction of zoonotic cutaneous leishmaniasis (ZCL) cases were evaluated in the studied ...endemic foci of Fars province, southern Iran, during 2016 to 2017.
Methods: Based on available data on disease circumstances collected from Center for Disease Control (CDC) of Shiraz University of Medical Sciences, incidence of disease, and demographics of the natives, five villages were randomly selected among those with high and medium CL infection in Kharameh area. All villagers were checked by physical examination and the incidence rates of ZCL cases were recorded. IVM interventions were implemented. Indeed, these procedures consisted of fipronil systemic insecticide poison baits, indoor residual spraying (IRS), outdoor spraying of the patients’ houses, and the thermal fogging (three times) during peak periods of sand flies’ activities.
Results: After interventions, the incidence rates of ZCL decreased by 2.55% in Mehrabad village, in which all IVM methods were implemented. Similarly, the incidence of disease was reduced by 4.89% in Sofla and Moezabad villages, using exclusively fipronil poison baits. Besides, these incidence rates declined by 1.15% in two control villages of Soltan-Shahr and Abshor, where examination of the rodent reservoir hosts was performed.
Conclusion: Fipronil and IVM methods were advantageous in reducing the incidence rates of leishmaniasis, but it seems that the use of fipronil systemic insecticide as a poison bait against reservoir rodent was significantly more effective (P-Value=0.01).
In this study, which was conducted using descriptive survey method, five questions and two hypotheses were proposed. Research data which was extracted from 90 employees of Iran’s District 12 Grain ...Company using questionnaires was analyzed by T, ANOVA, Tukey, Chi-Square, and Jonckheere Tests. Motivational factors affecting the employees’ performance in Iran’s District 12 Grain Company were selected based on Herzberg's theory, and include fame, growth and advancement, the job nature, responsibility and success. Cultural factors affecting the employees’ performance in this company were selected based on Robbins’ theory, and include attention to details, challenging spirit, attention to the employees, attention to the results, attention to the team, innovation, and stability. Moreover, the research results show that performance evaluation has affected the performance of the employees in Iran’s District 12 Grain Company, and the current evaluation system is acceptable by the employees. In addition, the order of importance for the factors affecting the employees’ performance in Iran’s District 12 Grain Company are as follows: 1)the job nature; 2)fame; 3)responsibility; 4)growth and advancement; and 5)success. The order of importance for cultural factors affecting the employees’ performance are as follows: 1)innovation; 2)stability; 3)attention to the employees; 4)attention to the results; 5)attention to the team; 6)attention to details; and 7) challenging spirit.
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