Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie最新文献

{"title":"Microstructural influences on the damage evolution and kinetics of high temperature hydrogen attack in a C-0.5 Mo welded joint","authors":"CC Pretorius, R. Mostert, T. Mukarati, VM Mathoho","doi":"10.36303/satnt.2021cosaami.40","DOIUrl":"https://doi.org/10.36303/satnt.2021cosaami.40","url":null,"abstract":"In the refining industry, steels can be susceptible to a damage mechanism known as high temperature hydrogen attack (HTHA). The detection of damage in such structures through non destructive testing (NDT) requires insight into the damage development in various parts of welded joints. Once damage is detected, the tracking of the damage progression and estimation of remaining life is problematic. The performance of C-0.5 Mo steels in such environments is also variable, and the current tendency is to regard the HTHA resistance of C-0.5 Mo as similar to that of carbon steels. The current investigation explores the possibility of using high-temperature capsule strain-gauges for the in-situ evaluation of swelling – which generally accompanies HTHA in susceptible steels – and, thereby, evaluate the development and kinetics of HTHA damage for a C-0.5 Mo steel welded joint. Specimens were prepared representing the base metal (BM), the HAZ region, both fine-grained and coarse-grained, and the weld-metal (WM). The specimens were exposed to hydrogen at 200 bar at a temperature of 500 °C in an autoclave, with certain specimens fitted with high-temperature strain gauges; i.e. instrumented test labelled as IWM, IHAZ and IBM. Metallographic evaluation of the specimens – regarding the three locations mentioned – were performed; with exposure times reflecting both incipient and advanced damage. In the case of the base metal and the fine grained HAZ, and after pronounced damage, macrocracks were observed. The orientation and location of these cracks were aligned with the rolling direction, and the cracks were evident in the through-thickness plane of the plate. It was found that the reason for this observation was due to preferential damage accumulation within banded regions, where high concentrations of carbides were observed. A sigmoidal equation was developed that described the swelling kinetics of the HAZ. The expression of swelling-induced strain rate (SISR) versus time showed a low initial SISR until incipient damage is formed, followed by accelerated attack. The peak SISR was observed midway through the damage evolution, where after the SISRs decreased as the presense of carbides – that feed the methane reaction – diminishes. It is proposed that the attachment of the encapsulated strain gauges to structures or components where HTHA damage is suspected, will assist in the tracking of damage and the estimation of remaining life; if used in conjunction with the developed sigmoidal equation.","PeriodicalId":22035,"journal":{"name":"Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76219535","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Corrosion performance of Ti-Cu alloys targeted for biomedical applications","authors":"Nde Masia, M. Smit, IA Mwamba, L. Fowler, L. Chown, S. Norgren, C. Öhman-Mägi, N. Hashe, L. Cornish","doi":"10.36303/satnt.2021cosaami.45","DOIUrl":"https://doi.org/10.36303/satnt.2021cosaami.45","url":null,"abstract":"The Thermo-Calc™ program and TTTI3 database were used to predict the phases in Ti-Cu with 5, 25, and 40 wt% Cu. Based on the predicted results, experimental work was conducted and the Ti-Cu alloys were produced in a button arc furnace, and characterised in the as-cast and the annealed condition (900°C) followed by water quenching. Microstructures and compositions were determined using an electron probe micro-analyser, and the phases were identified by X-ray diffraction. The corrosion performance was measured by potentiodynamic polarisation in a phosphate buffered saline solution at 37 °C at 7.4 pH while purging with nitrogen gas. The Ti-5Cu and Ti-25Cu alloys comprised (αTi) and Ti2Cu phases, the Ti-40Cu alloy comprised Ti2Cu and TiCu. Although the addition of copper decreased the corrosion performance by down to 75%, the corrosion rates were still within the acceptable range (0.02-0.13 mm/y) for biocompatibility of metallic implants. Annealing at 900 °C did not improve the corrosion performance.","PeriodicalId":22035,"journal":{"name":"Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie","volume":"60 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80574690","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Computational modelling studies for high temperature monazite systems","authors":"L. Motsomone, RG Diale, P. Ngoepe, R. Koen, H. Chauke","doi":"10.36303/satnt.2021cosaami.11","DOIUrl":"https://doi.org/10.36303/satnt.2021cosaami.11","url":null,"abstract":"Monazite is widely considered as a potential source of fissile feedstock for nuclear power generation, as it generally contains significant quantity of thorium (Th), uranium (U) and rare earth elements (REEs) within the mineral ore structure. Currently, a new process of high-temperature cracking of monazite is under development to improve the liberation of these cations from the robust monazite lattice. The current process for extraction of the REEs from the mineral involves complicated processes which makes use of harsh chemicals. These process therefore has significant scope for optimisation. With this in mind, the stability of monazite systems, t-CeSiO4 and m-LaSiO4 was investigated using first-principle calculation employing density functional theory (DFT) to gain a better understanding of the inherent molecular structures and the influence of temperature on conformation. The calculated lattice parameters for the model of t-CeSiO4 were found to be in good agreement with the experimental values (within 3%) and deemed a sufficient m-LaSiO4 of the system to be exposed to simulated reaction conditions. The elastic properties suggested that t-CeSiO4 is the more stable structure compared to m-LaSiO4 structure at 0 K. Semi-empirical embedded atom method interatomic potentials incorporated in the LAMMPS code were also employed to investigate the lattice expansion of t-CeSiO4 at high temperatures. It was found that calculated a and b lattice parameters expand with a linear ratio to a temperature of 2200 K whereas the c parameter was found to contract in the same temperature range. The findings provided an in depth understanding of the monazite molecular structure change at higher temperatures that may be helpful in plasma cracking optimisation experimental methodologies.","PeriodicalId":22035,"journal":{"name":"Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77305400","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Reconditioning of ti6al4v powder through an inductively coupled plasma for direct metal laser sintering","authors":"N. Nkhasi, W. du Preez, H. Bissett","doi":"10.36303/satnt.2021cosaami.21","DOIUrl":"https://doi.org/10.36303/satnt.2021cosaami.21","url":null,"abstract":"Ti6Al4V is commonly used in the aerospace, medical and automotive industries due to its high strength-to-weight ratio and excellent corrosion resistance properties. Interstitial impurities in Ti6Al4V powder, particularly oxygen, nitrogen, hydrogen and iron, have an impact on mechanical properties. After Ti6Al4V powder has been re-used several times in direct metal laser sintering build processes, it will eventually reach its end of life due to its physical and chemical properties deteriorating out of specification. Such powder can be reconditioned using an inductively coupled plasma system. In this study, the reconditioning of the contaminated powder was done using an inductively coupled plasma system and characterisation of the Ti6Al4V powder was done before and after reconditioning. Conclusions are drawn on the feasibility of utilising an inductively coupled plasma system for reconditioning of contaminated Ti6Al4V powder.","PeriodicalId":22035,"journal":{"name":"Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie","volume":"57 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73083035","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Study of wear performance of wheel and rail steels under dry sliding conditions","authors":"T. Leso, CW Siyayisa, R. Mostert, J. Moema","doi":"10.36303/satnt.2021cosaami.09","DOIUrl":"https://doi.org/10.36303/satnt.2021cosaami.09","url":null,"abstract":"The demand for efficient railway services has significantly increased in the past years due to an increased demand for the high-speed transportation of goods with high loads. The increase in loads and velocities has resulted in increased problems associated with rolling contact fatigue (RCF), rolling and sliding wear on the wheel and rail materials causing a reduction of service life of wheel/rail systems. Rail operating companies spend significant funds in maintenance and replacing damaged rails and wheels caused by wear. In addition, unscheduled maintenance due to wear and RCF often lead to poor availability of railway networks. For this study, dry sliding wear was investigated on wheel and rail steels using RTEC Multi-Function Tribometer. The results demonstrated that the rig was successful in simulating sliding wear, and that the fractions of the wear components could be varied, and it also provided instrumentation. Information on coefficient of friction against sliding distance and applied force were obtained which were used to compare sliding wear performance of both wheel and rail steels. The wheel was found to perform better than the rail under the same conditions due to its high initial hardness values and smaller interlamellar spacing.","PeriodicalId":22035,"journal":{"name":"Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie","volume":"196 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77416128","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Using site occupation disorder to build bulk structures of Ni1-xAlx","authors":"C. Thesner, A. Falch, G. Cornelia, CE Van Sittert","doi":"10.36303/satnt.2021cosaami.33","DOIUrl":"https://doi.org/10.36303/satnt.2021cosaami.33","url":null,"abstract":"Raney nickel shows potential as an electrocatalyst for the oxygen evolution reaction (OER). However, the catalytic activity of Raney nickel varies with its properties. These properties are related to the composition of the bimetallic precursor used to synthesise Raney nickel. The bimetallic precursor consists of a combination of bimetallic phases. Various studies have been done on the well-known bimetallic phases, namely, Ni2Al3, NiAl and NiAl3. However, to get a more comprehensive understanding of the influence of the bimetallic precursor on the properties of Raney nickel, a larger spectrum of bimetallic phases needs to be evaluated. In this study, the Site Occupation Disorder (SOD) program was used to build solid-state structures (bimetallic phases) with various Ni1-xAlx bimetallic ratios. These Ni1-xAlx bimetallic phases were evaluated, and unique configurations for each Ni1-xAlx bimetallic ratio were obtained. The unique configurations were geometrically optimised using the General Utility Lattice Program (GULP) at 0K. These optimised unique configurations were thermodynamically evaluated over a range of 0.1K – 1200K, and the most stable configurations with a probability higher than 10% were identified. This study found that the stable non-homogeneous configurations fall within a range of 20% - 80% Ni content. A weight average combination of these configurations of the bimetallic phases will produce a non-homogeneous precursor with an average Ni content of 20% - 80%, which is in close agreement with experimental results. The approach in this study enables researchers to obtain a larger, repeatable spectrum of bimetallic phases for the investigation of Raney nickel precursors.","PeriodicalId":22035,"journal":{"name":"Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie","volume":"10 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82313181","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Effect of different simulated metal dusting environments on austenitic Alloys 602CA and 800","authors":"F.M.L. Mulaudzi, L. Cornish, G. Slabbert, SJ Moema, MJ Papo","doi":"10.36303/satnt.2021cosaami.34","DOIUrl":"https://doi.org/10.36303/satnt.2021cosaami.34","url":null,"abstract":"Metal dusting processes and associated filamentous carbon formation were studied on austenitic Alloys 602CA and 800 after exposure to 18.9%CO-79.1%H2-2%H2O and 25%CO-70%H2-5%H2O (vol.%) gas mixtures at 650°C. The alloys were studied by visual examination, optical microscopy, scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), Raman spectroscopy and X-ray diffraction (XRD). Alloy 602CA was more resistant to metal dusting than Alloy 800. SEM imaging of the surfaces showed that Alloy 800 suffered metal attack at 168 h, whereas Alloy 602CA suffered minor attack only after 336 h. Coke deposits increased on Alloy 800 with increased exposure, and there was little coke deposited on Alloys 602CA from after 336 h. Raman spectroscopy confirmed graphite by the characteristic D- and G-peaks.","PeriodicalId":22035,"journal":{"name":"Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie","volume":"12 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88661532","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The effect of laser surface re-melting on the surface roughness and micro-hardness of selective laser melting (SLM) fabricated Ti-6Al-4V samples","authors":"G. Molatlhegi, S. Hoosain, A. Popoola, N. Malatji, S. Pityana","doi":"10.36303/satnt.2021cosaami.35","DOIUrl":"https://doi.org/10.36303/satnt.2021cosaami.35","url":null,"abstract":"Ti-6Al-4V is favourable due to its exquisite properties for example, low modulus, light weight, excellent strength, and corrosion resistance. Despite the excellent properties of the material, the fabrication process of titanium components is challenging due to the poor final surface quality components caused by non-uniform powder distribution during additive manufacturing (AM) using selective laser melting (SLM) process. SLM process produces fully denser parts with better mechanical properties compared to the bulk materials, although the surface quality is poor. This work aims to study the effect of laser surface re-melting (LSM) on the hardness and surface properties of Ti-6Al-4V alloy. The fabricated Ti-6Al-4V sheet was re-melted by a 3 kW IPG Fiber laser. Microstructural evaluations of the Ti-6Al-4V sheet were characterized using an optical microscope. Micro-hardness and surface roughness measurements were determined by means of an HV Vickers tester under an applied load of 300g and load time of 10s and MarSurf PS1 roughness tester machine respectively. Microstructural evolution and hardness properties were all examined before and after the LSM treatment. The experimental results showed the formation of martensitic structure on the areas treated. Micro-hardness depth profiling results showed an average increase of 15–25% which was higher compared to the average hardness of the as-received. The results indicated that the roughness measurements lowered when both the residence time and irradiance increase. Laser surface re-melting treatment showed an improvement of the microstructural modifications and hardness properties therefore, the process can be used to modify the component’s surface for reliable and best surface finish.","PeriodicalId":22035,"journal":{"name":"Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie","volume":"8 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87533504","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Tracking the railway line in-service behaviour through metallurgical and mechanical property characterisation","authors":"A. Mwamba, A. Mabeba, J. Moema, M. Phasha","doi":"10.36303/satnt.2021cosaami.46","DOIUrl":"https://doi.org/10.36303/satnt.2021cosaami.46","url":null,"abstract":"Wear, contact-impact, fatigue and corrosion properties are important factors initiating rail track degradation and are composition dependent. This work focuses on the effect of chromium content on the metallurgical and mechanical properties of the the rail steels. Two medium steel railway tracks differing in their chromium content, alloy MS02 with 0.02 wt% Cr and alloy MS03 containing 0.72 wt% Cr, were characterised in order to predict their in-service performance as a function of their chemical composition.\u0000\u0000The microstructural analysis revealed in MS02 a relatively coarser grain size, consisting of pearlite and grain boundary ferrite. MS03 showed a fully pearlitic structure with no grain boundary ferrite. The average distance between cementite lamella in rail MS03 is shorter than that in MS02. The Rockwell C hardness values of MS02 were lower than those of MS03 which is in agreement with the microstructural analysis. As expected, a finer pearlitic structure observed in rail MS03 resulted in a superior tensile and impact properties as compared to MS02.\u0000\u0000These data indicate that MS03 with a fully pearlitic structure gives a better wear resistance and higher strength than MS02 and, it is anticipated to give a better corrosion and oxidation resistance due to higher chromium content.","PeriodicalId":22035,"journal":{"name":"Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie","volume":"3 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80688731","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"First principles study of phase stability and elastic properties of Ti94Mo6-xZrx (where x: 2 ≤ x ≥ 5) for biomaterials","authors":"VC Mnisi, Methias Sithole, R. Modiba","doi":"10.36303/satnt.2021cosaami.29","DOIUrl":"https://doi.org/10.36303/satnt.2021cosaami.29","url":null,"abstract":"Elastic modulus is a very important physical aspect for biomaterials which is impartial to various replacements as artificially hip joints, bone plate, and gum implants since it measures the material’s resistance to be deformed elastically. This is because “stress shielding effect” will result in the re absorption of natural bone and the implant loosening if a great difference of elastic modulus exists between the biomaterial implant and human bone. In this study first principle calculations have been performed to study the β-phase of Ti-Mo-Zr system to improve its elastic moduli. The phase stability of Ti94Mo6-xZrx (where x: 2 - 5) alloys was investigated with respect to their equilibrium lattice parameters, elastic constants and the density of states. The results suggest that the Youngs moduli can be significantly enhanced with the addition of Zirconium (Zr) and decreasing Molybdenum (Mo) concentration while keeping Titanium (Ti) constant, which indicates phase stability. The Youngs modulus of structures Ti94Mo6-xZrx was found to be between -2GPa and 24GPa. The electronic density of states curves also showed phase stability for structures Ti94Mo4Zr2 since it was observed that the Fermi level is located close to the valley of the pseudogap. The results obtained are in agreement with the available experimental data and showed a similar trend. The study has shown that Zr has improved the elastic properties and the phase stability of Titanium alloy.","PeriodicalId":22035,"journal":{"name":"Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie","volume":"83 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79692743","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}