•The effects of building orientation, heat treatment, and surface finish on the fatigue strength of SLM steels.•The effects of manufacturing parameters on the fatigue strength of SLM steels.•Defects ...and crack-microstructure interactions in SLM steels based on their manufacturing parameters.•Knowledge gaps in the field of fatigue characteristics of SLM steels and necessity of further study in this regards.
Additive manufacturing is extending its influence on various modern industries, including automobile, aerospace, aviation, and maritime. This is specifically true for selective laser melting since it is capable of manufacturing dense parts from metal and alloy powders. Thus, the performance of materials processed by selective laser melting has become the focus of many studies recently. However, their fatigue endurance is yet to be understood comprehensively, and few studies have been carried out on this topic thus far. The lack of understanding is often attributed to the considerable number of manufacturing parameters, which also hinders employing selective laser melting for typical industrial applications. Among the various materials processed by selective laser melting, steel is one of the most attractive ones to manufacturers due to its broad range of properties and applications. This paper aims to describe the studies carried out on the fatigue properties of diverse types of steel manufactured by selective laser melting. It also reviews the parameters which are recognized to be effective on the fatigue behaviour of these steels. These parameters include building orientation, heat treatment, surface quality, energy density, and service condition of the final product. Recent studies on selective laser melting along with the variety of its influential parameters on the fatigue strength highlight a knowledge gap towards reaching a comprehensive understanding of the fatigue behaviour of steels manufactured by this process. Based on this fact, some of these gaps are discussed as the potential topics for the future studies in the field of additive manufacturing at the end of this review.
Additive manufacturing, a common example of which is 3D printing, has become more prevalent in recent years with it now being possible to form metallic structural elements in this way. There are, ...however, limited available experimental data on the material behaviour of powder bed fusion (PBF) additive manufactured metallic structural elements and no existing data at the cross-section level; this is addressed in the present paper through a series of tests on additive manufactured stainless steel material and cross-sections. Tensile and compressive coupon tests were used to assess anisotropy, symmetry of stress-strain behaviour and the influence of building direction on the material properties. The yield and ultimate tensile strengths were seen to generally decrease in magnitude with increasing build angle, while a reduction in ductility was observed in some building orientations, and the Young's moduli were typically insensitive to the build angle. The structural behaviour of PBF additive manufactured cross-sections was investigated through a series of square hollow section (SHS) stub column tests, and the results compared with conventionally produced stainless steel SHS. The generated test results have been used to evaluate the applicability of existing design guidance for conventionally produced sections to additive manufactured sections.
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•Tensile and compressive additively manufactured PH1 martensitic and 316L austenitic stainless steel coupon tests reported.•The first structural tests on additively manufactured 316L stainless steel structural members have been undertaken.•The results are compared against conventional stainless steel stub columns from the literature.•The predictions from Eurocode 3 and the continuous strength method are appraised.
Laser powder bed fusion (LPBF) is a metal additive manufacturing technique involving complex interplays between vapor, liquid, and solid phases. Despite LPBF's advantageous capabilities compared to ...conventional manufacturing methods, the underlying physical phenomena can result in inter-regime instabilities followed by transitions between conduction and keyhole melting regimes - leading to defects. We investigate these issues through operando synchrotron X-ray imaging synchronized with acoustic emission recording, during the remelting processes of LPBF-produced thin walls, monitoring regime changes occurring under constant laser processing parameters. The collected data show an increment in acoustic signal amplitude when switching from conduction to keyhole regime, which we correlate to changes in laser absorptivity. Moreover, a full correlation between X-ray imaging and the acoustic signals permits the design of a simple filtering algorithm to predict the melting regimes. As a result, conduction, stable keyhole, and unstable keyhole regimes are identified with a time resolution of 100 µs, even under rapid transitions, providing a straightforward method to accurately detect undesired processing regimes without the use of artificial intelligence.
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•The research novelty lies in evaluating the tribological and biological properties of Nickel Free Stainless Steel (NiFSS) produced through laser bed powder diffusion for metals ...(PBF-LB/M) additive manufacturing.•Optimized process parameters for PBF-LB/M fabrication of NiFSS resulted in samples with a relative density of 98.469% and fully ferritic microstructure in the as-built state.•Tribological experiments assessed NiFSS at constant load and sliding speed using an automated Bio-Tribometer, showing promising friction coefficients and wear rates relevant to implant applications.•NiFSS exhibited reduced Coefficient of Friction and wear rates compared to PBF-LB/M built austenitic 316L SS, attributed to its superior hardness and elastic modulus.•Biocompatibility testing with pre-osteoblastic MC3T3-E1 cells indicated better cell viability on PBF-LB/M built NiFSS compared to PBF-LB/M built 316L SS.•The present study suggests the potential of PBF-LB/M fabricated NiFSS for use in biomedical devices, particularly in joint arthroplasty applications.
Due to the risk of releasing carcinogenic nickel ions from conventional 316L stainless steel under a corrosive human body environment, a new variant of steel termed nickel-free stainless steel (NiFSS) has been investigated. The present study investigates the tribological properties and biocompatibility of NiFSS manufactured via laser powder bed fusion (PBF-LB/M). The ferritic NiFSS exhibited significantly lower coefficient of friction (0.08 to 0.28) and wear rate (1.60 × 10-6 mm3/Nm to 6.60 × 10-6 mm3/Nm) compared to reported values for austenitic 316L SS, under both dry and simulated body fluid (SBF) conditions and various sliding geometries. This improvement is attributed to the superior hardness (3.394 ± 0.1340 GPa) and elastic modulus (238 ± 9.0797 GPa) of NiFSS. To assess the biocompatibility, the viability of mouse pre-osteoblastic MC3T3-E1 cells was evaluated with an Alamar Blue assay when the cells were cultured on top of PBF-LB/M built NiFSS and 316L SS samples. The results indicated that even though cell growth was most optimal on regular cell culture plastic, cell viability was better maintained on PBF-LB/M built NiFSS compared to 316L SS. Therefore, the results of the present study propose that PBF-LB/M fabricated NiFSS holds promise for application in biomedical devices for joint arthroplasty.
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•Microstructural analysis reveals narrow weld regions and HAZ generated by employed laser welding.•Anisotropy of additively manufactured base material and effects of energy input of ...laser welding are examined.•Local and global stress-strain relationships are determined using non-contact digital image correlation method.•Results of tensile tests on additively manufactured stainless steel coupons with laser welded joints are presented.•Variations in the mechanical properties are correlated with differences in internal microstructure.
Powder bed fusion (PBF) is a commonly employed metal additive manufacturing (AM) process in which components are built, layer-by-layer, using metallic powder. The component size is limited by the internal build volume of the employed PBF AM equipment; the fabrication of components larger than this volume therefore requires mechanical joining methods, such as laser welding. There are, however, very limited test data on the mechanical performance of PBF metal with laser welded joints. In this study, the mechanical properties of PBF built 316L stainless steel parts, joined together using laser welding to form larger components, have been investigated; the microstructure of the components has also been examined. 33 PBF 316L stainless steel tensile coupons, with central laser welds, welded using a range of welding parameters, and with coupon half parts built in two different orientations, were tested. The porosity, microhardness and microstructure of the welded coupons, along with the widths of the weld and heat-affected zone (HAZ), were characterised. The PBF base metal exhibited a typical cellular microstructure, while the weld consisted of equiaxed, columnar and cellular dendrite microstructures. Narrow weld regions and HAZs were observed. The PBF base metal was found to have higher proof and ultimate strengths, but a similar fracture strain and a lower Young’s modulus, compared with conventionally manufactured 316L stainless steel. The strengths were dependent on the build direction – the vertically built specimens showed lower proof strengths than the horizontal specimens. The laser welds generally exhibited lower microhardness, proof strengths and fracture strains than the PBF base metal which correlated with the observed structure. This work has demonstrated that PBF built parts can be joined by laser welding to form larger components and provided insight into the resulting strength and ductility.
This study concerns the weldability of dissimilar Ultra high-strength steel (UHSS) and advanced high-strength steel (AHSS), which is used in the modern machine industry. The materials offered ...superior strength as well as relatively low weight, which reduces microstructure contamination during a live cycle. The choice of the welding process base of the base material (BM) and welding parameters is essential to improve the weld joint quality. S700MC/S960QC was welded using a gas metal arc welding (GMAW) process and overmatched filler wire, which was performed using three heat input (7, 10, and 15 kJ/cm). The weld samples were characterized by a Vickers-hardness test, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). The test reveals a decrease of softening areas in the HAZ and the formation of the stable formation of Bainite-Ferrite for S700MC and Bainite-martensite for S960QC when the heat input of 10 kJ/cm is used. It is recommended to use the GMAW process and Laser welding (Laser beam-MIG), with an optimal welding parameter, which will be achieved a high quality of manufacturing products.
Multiparametric Magnetic Resonance Imaging (mpMRI) has been proposed to add value in the diagnostic pathway of bladder cancer (BC). We wanted to evaluate the performance of mpMRI for muscle-invasion ...detection in BC patients using a subjective MRI visual T-category and the Vesical Imaging-Reporting and Data System (VI-RADS) score.
This single centre clinical trial included 45 patients with suspected BC (ClinicalTrials.gov Identifier: NCT02662166). All patients had mpMRI prior to transurethral resection of bladder tumour (TUR-BT). The imaging was correlated to histopathological findings. Two individual radiologists evaluated all the mpMRI images. A binary cut-off point for the detection of muscle-invasion in the MRI visual T-category was defined between T1 and T2 and the VI-RADS cut-off score was 3. Cohen's Kappa values were used to evaluate the agreement between the two radiologists. Sensitivity, Specificity, Area Under Receiver Operator Characteristics Curve (AUC), Positive Predictive Value (PPV) and Negative Predictive Value (NPV) were calculated to evaluate the performance of both radiologists separately.
AUC values for reader A and B using the MRI visual T-category were 0.76 and 0.56, while the corresponding values for VI-RADS were 0.63 and 0.57, respectively. There was no statistically significant difference between the radiologists nor the reporting systems (p > .05) in the detection of muscle-invasion. The inter-reader agreement was substantial (0.61-0.80).
Both the subjective MRI visual T-category and VI-RADS score had only a low to moderate accuracy for the detection of muscle-invasion in BC with no statistically significant difference between the reporting systems.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Population-based survival results after radical cystectomy (RC) are limited. Our objective was to report short and long-term survival results after RC for bladder cancer from Finland in a ...population-based setting.
The Finnish National Cystectomy Database containing retrospectively collected essential RC data covering the years 2005-2017 was combined with the survival data from the Finnish Cancer Registry. Kaplan-Meier plots were used to estimate survival and the survival graphs were illustrated according to the final pathological staging. Centers were divided according to operational volume, and the results were then compared using Pearsons's Chi-squared test.
A total of 2047 patients were included in the study. 30-, and 90-day mortality was 1.3%, and 3.8%, respectively. The OS of the entire RC population at 5- and 10 years was 66% and 55%, and CSS was 74% and 72%, respectively. Center volume did not significantly associate with surgical mortality or long-term survival. The 5- and 10-year OS according to pT-category was 87% and 74% for pT0, 85% and 69% for pTa-pTis-pT1, 70% and 58% for pT2, 50% and 42% for pT3 and 41% and 30% for pT4. The corresponding 5- and 10-year CSS rates were 96% and 93% for pT0, 91% and 90% for pTa-pTis-pT1, 78% and 75% for pT2, 56% and 55% for pT3 and 47% and 44% for pT4. The 5- and 10-year OS rates in patients with no lymph node metastases (pN-) were 74% and 62%, and CSS 82% and 80%, respectively. If lymph nodes were positive (pN+), the corresponding OS rates were 44% and 34% and CSS 49% and 48%, respectively.
RC survival results have improved in contemporary series and are associated with the pTNM-status. The nationwide results from Finland demonstrate outcome comparable to high volume single-center series.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Selective Laser Melting (SLM) is an advanced Additive Manufacturing (AM) technique for the 3D printing of metals. SLM process parameters and different types of defects that may appear during the ...manufacturing process affect the quality of the final product. Setting laser parameters and online defect detection contributes to improving the quality of parts fabricated through SLM technology. In this study, the effect of the process parameters on the properties of the product built by the SLM process was investigated, and an in-situ monitoring platform was developed to detect two types of defects during the SLM process. Different samples were built from stainless steel AISI 316 L powder, utilizing various laser process parameters. Using microscopy imaging technique, the melt structure features of the constructed samples were tested, and the results were analyzed. The dependency of porosity formation on laser process parameters and scan strategy was investigated. Moreover, hardness test was performed for all built samples. The platform developed for in-situ monitoring purposes includes an AM machine equipped with pulsed laser, camera, illumination system, and powerful industrial computer equipped with Cameral Link Adapter, FPGA, and Real-Time (RT) modules. An algorithm was designed using LabVIEW ® software based on Particle Analysis (PA) to cease the process in the event of detection of defect in any fused layers. The first defect was caused by changing the laser spot diameter, which altered the energy intensity of the laser on the surface, and the second defect was created by the uneven thickness of powder on the platform. The monitoring system detected both defects and stopped the process immediately according to the designed algorithm. Images were taken from the melting process layer by layer using a high-performance camera.
The applications of thermomechanically processed ultra-high strength steels (UHSS) are rapidly increasing, and welding these UHSSs seems inevitable in steel structures. However, welding heat causes ...unwanted microstructural transformations in the heat-affected zone (HAZ). Due to the localized nature of these changes throughout the HAZ, evaluating the true stress–strain values of these localized HAZ subzones is essential to improve the accuracy of analytical or numerical models. Hence, this study utilized experimental thermal simulations to replicate HAZ subzones of two types of UHSSs, i.e., direct-quenched S960 and quenched-and-tempered S1100, and employed tensile test in conjunction with digital image correlation to plot the true stress–strain and hardening curves of the subzones. Both UHSSs manifested similar trends but with various fluctuations in their hardening capacities throughout their HAZ subzones. Next, hardening parameters from Hollomon, Voce, and Kocks-Mecking approaches were extracted by fitting the experimental results with the semi-empirical equations. For both UHSS types, the Voce approach, on average, was more accurate in modeling the plastic deformation. Also, hardening parameters achieved via the Voce approach’s fittings agreed with the parameters from Kocks-Mecking plots; this consistency pointed to the predictability of the plastic flow and hardening behavior of both UHSS types. According to the microstructural investigations, the hardening behavior of the investigated HAZ subzones depended on two types of microstructure constituents: ferritic and lath-like features. Ferritic features dominantly governed the plastic flow and hardening near the fusion line, while by getting distant from the fusion line, the lath-like features became more dominant.
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