Additive manufacturing (AM) especially laser additive manufacturing (LAM), a novel manufacturing technique of layer-by-layer forming according to geometric model, provides a decent option for ...materials processing. It owns advantages of rapid prototyping, customization, high material utilization, and the ability to form complicated structures. This paper reviews popular LAM techniques of selective laser sintering/melting, laser metal deposition and laser direct writing. The development status of metallic materials including pure metal, steel, superalloy, titanium and aluminum alloy is presented. The challenges and application limitations of LAM are involved and the development trend in the future is forecasted. In summary, this paper gives an overview of metal LAM expecting to made helpful suggestions on future research and development.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Laser cladding is a promising surface modification and repair technology for fabricating Inconel 718 parts. However, laser cladding may produce coarse grains and brittle Laves phase, leading to a ...significant decrease in performance. The application of high-intensity ultrasonic vibration in laser cladding is able to refine grain and reduce Laves phase. This study investigates the distribution characteristics and the evolution mechanism of the grains and Laves phase in laser cladding with high-intensity ultrasonic vibration. The effects of high-intensity ultrasonic vibration on alteration of grain characteristics and the reduction of Laves phase were analyzed and discussed through ultrasonic vibration-assisted laser cladding experiments. Results indicate that high-intensity ultrasonic vibration promoted a columnar-to-equiaxed transition, and reduced the grain size from 75.6 μm to 48.8 μm. Furthermore, the Laves phase had a decrease of 47.1% in the volume fraction, and transformed from a long-striped shape into a fine granular shape, leading to a more homogeneous distribution of elements in Laves phase. The change in the grains and the Laves phase is attributed to dendrite fragmentation and inhibition of element segregation by nonlinear effects of ultrasound including cavitation and acoustic streaming. The findings of this study confirm the significant benefits of applying high-intensity ultrasonic vibration in laser cladding and provide insight into the underlying evolution mechanisms of high-intensity ultrasonic vibration for grains and Laves phase.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Agricultural machinery socialization services are an important means of alleviating poverty and promoting agricultural modernization. Based on 2750 items of survey data from farmers in Henan ...Province, this paper empirically tests the impact and mechanism of agricultural machinery socialization service adoption on the relative poverty of farmers by using a binary logit model and mediation effect model. The results show that the adoption of agricultural machinery socialization services has a significant negative impact on the relative poverty of farmers. The reduction in natural risk plays an intermediary role in the impact of the adoption of agricultural machinery socialization services on the relative poverty of farmers. The size of the household labor force and the land operation scale affect the poverty reduction effect of agricultural machinery socialization services. It can be seen that in the relative poverty governance stage, we should improve the development of the agricultural machinery socialization service system, enhance the risk resistance of farmers, build a supporting system for farmers’ employment skills training, and encourage an orderly connection between the large-scale operation of agricultural land and the large-scale operation of services so as to fully realize the poverty reduction role of agricultural machinery socialization services.
Reptiles are asymptomatic carriers of
spp. Reptile-associated
infections have been noticed as a significant contributor to overall human salmonellosis. However, it remains unclear regarding the ...prevalence of reptile-associated
in China.
Fecal and gastrointestinal mucosal samples were taken from 104 snakes, 21 lizards, and 52 chelonians and cultured on selective medium. The positive clones were validated and annotated by biochemical screening and multiplex PCR verification. In addition, the antibiotic resistance of identified
isolates was detected and followed by cytotoxic activity detection on human colon cells via co-culturation.
The overall prevalence of
in reptiles was 25.99%, with rates of 30.77%, 47.62%, and 7.69% in snakes, lizards, and chelonians, respectively. Further, all isolates showed variable drug-resistant activity to 18 antibiotics, of which 14 strains (30.43%) were resistant to more than eight kinds of antibiotics. More than half of isolated
strains were more toxic to host cells than the standard strain, SL1344. Whole genome sequencing (WGS) results showed that all lizard-associated strains belong to 4 serovar types, and 7 of them fall into the highly pathogenic serovars "Carmel" and "Pomona."
Our results highlight the potential threat of zoonotic salmonellosis from captive reptiles in the Beijing area of China.
Full text
Available for:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
•The developments of various material systems on laser surface alloying on aluminum alloys are reviewed.•The influences of different processing parameters are discussed.•The microstructure and ...surface properties of alloyed layer are analyzed.•The existing problems and the corresponding solutions are elucidated and the future developments are predicted.
Aluminum and its alloys have been widely used in aerospace, automotive and transportation industries owing to their excellent properties such as high specific strength, good ductility and light weight. Surface modification is of crucial importance to the surface properties of aluminum and its alloys since high coefficient of friction, wear characteristics and low hardness have limited their long term performance. Laser surface alloying is one of the most effective methods of producing proper microstructure by means of non-equilibrium solidification which results from rapid heating and cooling. In this paper, the influence of different processing parameters, such as laser power and scanning velocity is discussed. The developments of various material systems including ceramics, metals or alloys, and metal matrix composites (MMCs) are reviewed. The microstructure, hardness, wear properties and other behaviors of laser treated layer are analyzed. Besides, the existing problems during laser surface treatment and the corresponding solutions are elucidated and the future developments are predicted.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Display omitted
•In-situ TiB2-TiC reinforced Fe-Al composite coatings were generated by laser surface alloying on 6061 aluminum.•When adding 30 wt. % Ti, TiC nucleated heterogeneously on the surface ...of short rod-like TiB2, forming TiB2/TiC composites.•The disregistry between (0001)TiB2 and (111)TiC planes was only 1.049 %, indicating an effective heterogeneous nucleation.•The average micro-hardness was 7 times higher than that of the substrate.•A 92.8 % reduction in the volume loss indicated a significant improvement in wear resistance.
To improve the wear resistance of 6061 aluminum alloy, we have reported the fabrication of in-situ TiB2-TiC reinforced Fe-Al composite coatings by laser alloying with Fe-based self-fluxing alloy, B4C and Ti mixed powder. Two Ti contents, which are 30 wt. % and 45 wt. %, in the alloyed coatings were investigated as comparisons, so that investigate phase compositions, microstructures and wear resistance of the alloyed coatings. Additionally, the disregistry between (0001)TiB2 and (111)TiC planes were calculated, of which the formation mechanism of TiB2/TiC composite structure was further analyzed. It was found that the alloyed coatings mainly consisted of TiB2, TiC, Fe4Al13, Cr2B, Cr7C3, Al3Ti and α-Al. With the addition of 30 wt. % Ti, we found that TiC nucleated heterogeneously on the surface of short rod-like TiB2, forming TiB2/TiC composites. The interface was well bonded with a low disregistry of 1.049 %. The average micro-hardness of the composite coating was larger than 7 times of the substrate with a high value of 520 HV0.2. Moreover, a 92.8 % reduction in the volume loss enunciated a significant enhancement in wear resistance. Nevertheless, with the increase of Ti component in the alloyed coating, the supportability of the metal matrix to the reinforcements decreased, resulting in a slight reduction of the micro-hardness and wear resistance.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
To improve the wear resistance of 6061 aluminum alloys, we reported the fabrication of Fe–Al coatings by laser surface alloying with mixed Fe and Al powders. The alloyed coatings mainly consisted of ...Fe
4
Al
13
, FeAl, Fe
3
Al and α-Al phases. Due to its high specific gravity, the Fe-rich melt segregated at the bottom of the molten pool during the laser process, and special microstructures characterized by a bright white stripe at the interfacial zone were formed. Additionally, the nonuniform exothermic reactions occurring along the width of the interfacial zone resulted in the formation of a rough sawtooth interface. The typical microstructures from the top layer to the interfacial zone of the alloyed coatings were investigated to explore the formation and solidification processes of the molten pool. Additionally, the microhardness of the coatings markedly improved with increasing Fe concentration in the mixed powders, reaching 720 HV
0.2
. Moreover, a 92.3% reduction in the volume loss of the 70Fe–30Al coating compared with that of the substrate significantly enhanced the wear resistance.
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
To improve the wear resistance of AA6061 aluminium alloy, Fe-based composite coatings were prepared by laser surface alloying with Fe-B
4
C or Fe-B
4
C-Ti mixed powders. Microstructures, phase ...compositions and wear properties were investigated. The results indicated that the coating fabricated with Fe-B
4
C was mainly composed of FeAl, Fe
3
Al, Fe
4
Al
13
, CrB, Cr
2
B, Cr
23
C
6
, Al
4
C
3
, (Fe, Cr) and α-Al phases. When adding Ti in the precursor powders, TiB
2
and TiC were also well detected. In-situ synthesised TiB
2
particles dispersed on the matrix in a hexagonal platelike structure or closely agglomerated and connected with each other to form a whole. The formation mechanism of TiB
2
in different morphologies was further discussed. Compared with the 6061 Al substrate, the micro-hardness of the alloyed coatings was improved to 5.7-6.5 times. With the addition of Ti, the wear volume loss reduced to 10% of that of the substrate, indicating a significant improvement in wear resistance.
Full text
Available for:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Magnesium alloys are the most promising implant materials due to their excellent biodegradability. However, their high degradation rate limits their practical application. In this study, we produced ...a calcium-phosphate (Ca-P) coating and a calcium-phosphate-silicon (Ca-P-Si) coating
via
one-step and two-step micro-arc oxidation processes, respectively. The microstructure and chemical composition of the MAO coatings were characterized using SEM, XRD and EDS. The degradation behaviors of the MAO coatings and the substrate were investigated using electrochemical techniques and immersion tests in simulated body fluid (SBF). The results show that the silicate was successfully incorporated into the Ca-P coating in the second MAO step, and this also increased the thickness of the coating. The Ca-P-Si coatings remarkably reduced the corrosion rate of the Mg alloy and Ca-P coating during 18 days of immersion in SBF. In addition, the bone-like apatite layer on the sample surface demonstrated the good biomineralization ability of the Ca-P-Si coating. Potentiodynamic polarization results showed that the MAO coating could clearly enhance the corrosion resistance of the Mg alloy. Moreover, we propose the growth mechanism of the MAO coating in the second step.
Magnesium alloys are the most promising implant materials due to their excellent biodegradability.
PDF
