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  • MDPI AG  (16)
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  • MDPI AG  (16)
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  • English  (16)
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  • 1
    Online Resource
    Online Resource
    Research on Underwater Wet Laser Self-Fusion Welding Process and Analysis of Microstructure and Properties of TC4 Titanium Alloy Weld
    MDPI AG ; 2022
    In:  Materials Vol. 15, No. 9 ( 2022-05-08), p. 3380-
    Details
    In: Materials, MDPI AG, Vol. 15, No. 9 ( 2022-05-08), p. 3380-
    Abstract: In order to explore the feasibility of underwater wet laser welding of the TC4 titanium alloy, research on the underwater laser self-fusion welding process was carried out. The weld structure and mechanical properties in both the air environment and the underwater environment were compared and analyzed. The results show that increasing the laser power and reducing the welding speed are beneficial to obtain a larger water depth threshold. Off-focus amount has little effect on water depth threshold; when the laser power is 3000 W and the welding speed is 5 mm/s, and the water depth exceeds 7 mm, a continuous weld cannot be formed. Compared with welding in the air, underwater welding has narrower weld width, smaller heat affected zone and finer crystal grains. The weld structure is mainly composed of α′ martensite and secondary acicular α′ phase, it is distributed in a net basket shape and the grain size at the top of the weld is finer. The hardness of the weld center is above 600 HV0.1, and the residual stress of the underwater welding weld is approximately symmetrically distributed. There is a large tensile stress along the welding direction at the weld, reaching 458 MPa. The larger residual tensile stress leads to the decrease of weld tensile strength, the tensile strength and elongation of the middle sample are only 52% and 77% of the base metal. Furthermore, the fracture mode is typical brittle fracture.
    Type of Medium: Online Resource
    ISSN: 1996-1944
    URL: Article
    DOI: 10.3390/ma15093380
    Language: English
    Publisher: MDPI AG
    Publication Date: 2022
    detail.hit.zdb_id: 2487261-1
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  • 2
    Online Resource
    Online Resource
    Microstructure and Mechanical Properties of Wire Arc Additively Manufactured MoNbTaWTi High Entropy Alloys
    MDPI AG ; 2021
    In:  Materials Vol. 14, No. 16 ( 2021-08-11), p. 4512-
    Details
    In: Materials, MDPI AG, Vol. 14, No. 16 ( 2021-08-11), p. 4512-
    Abstract: High-temperature resistant high-entropy alloys (HEAs) have attracted extensive attention due to their excellent thermodynamic stability and mechanical properties, especially at high temperatures. However, a highly effective method for large-size HEAs is still desirable but challengeable. This research reported a facile yet effective strategy for MoNbTaWTi HEAs via in-situ wire arc additive manufacturing (WAAM). The wire was MoNbTaWTi cable-type welding wire (CTWW) consisting of one center wire and seven twisted peripheral wires. Then, additive manufacturing of MoNbTaWTi high entropy alloys (HEAs) was accomplished, and various analytical techniques studied the microstructures and mechanical properties of the overlaying formed layers. X-ray diffraction showed the overlaying formed layers to contain a single disordered BCC solid solution phase with high-temperature structural stability. In addition, the single-phase BCC structure was maintained from 0 to 1400 °C. The bottom of the overlaying formed layers was made of columnar cellular structure, and the upper part resembled “cauliflower-like” fine dendrite and equiaxed crystal structure. The hardness of the overlaying formed layers averaged 533 HV0.2 at room temperature. At 1000 °C, the hardness was around 110 HV1, close to the value of Inconel 718 alloy (125 HV1). The compressive strength of the overlaying formed alloy layers displayed no sensitivity towards change in temperature from 500 to 1000 °C. As the temperature rose from 500 to 1000 °C, the compressive strength changed from 629 to 602 MPa, equivalent to only a 27 MPa decrease. The latter was much higher than the strength of Inconel 718 alloy at the same temperature (200 MPa).
    Type of Medium: Online Resource
    ISSN: 1996-1944
    URL: Article
    DOI: 10.3390/ma14164512
    Language: English
    Publisher: MDPI AG
    Publication Date: 2021
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  • 3
    Online Resource
    Online Resource
    Passive Wireless Dual-Tag UHF RFID Sensor System for Surface Crack Monitoring
    MDPI AG ; 2021
    In:  Sensors Vol. 21, No. 3 ( 2021-01-28), p. 882-
    Details
    In: Sensors, MDPI AG, Vol. 21, No. 3 ( 2021-01-28), p. 882-
    Abstract: The generation and propagation of cracks are critical factors that affect the performance and life of large structures. Therefore, in order to minimize maintenance costs and ensure personal safety, it is necessary to monitor key structures. The sensor based on ultra-high frequency radio frequency identification (UHF RFID) antenna has the advantages of passive wireless, low cost, and great potential in the field of metallic structure health monitoring. In this paper, aimed at the key parts of a metallic structure, a dual-tag system is used for crack monitoring. In conjunction with mode analysis, the principles of the sensing tag and the coupling principles of the dual-tag are analyzed. Considering that the dual-tag is placed in different methods, the effect of mutual coupling on the sensing performance of the tag is studied. The results show that the frequency of the sensing tag can be tuned by adding the interference tag, and the dual-tag sensor system has reasonable sensitivity. The results also provide potential guidance for the optimal placement of multiple tags in the near-field region.
    Type of Medium: Online Resource
    ISSN: 1424-8220
    URL: Article
    DOI: 10.3390/s21030882
    Language: English
    Publisher: MDPI AG
    Publication Date: 2021
    detail.hit.zdb_id: 2052857-7
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  • 4
    Online Resource
    Online Resource
    Copper-Based Composite Coatings by Solid-State Cold Spray Deposition: A Review
    MDPI AG ; 2023
    In:  Coatings Vol. 13, No. 3 ( 2023-02-21), p. 479-
    Details
    In: Coatings, MDPI AG, Vol. 13, No. 3 ( 2023-02-21), p. 479-
    Abstract: Copper (Cu)-based composite coatings have been widely applied in all kinds of important industry fields due to their outstanding comprehensive properties. The preparation temperature of a composite coating is the key factor affecting the properties, so the cold spray (CS) technology is characterized by low-temperature solid-state deposition, which ensures its emergence as the most promising technology for preparing the Cu-based composite coatings. In this paper, first, the principle of CS technology and the deposition mechanism of the coatings are introduced. On this basis, the deposition mechanism of Cu-based metal/ceramic composite coatings is further explored. Secondly, the effects of key CS process parameters (particle velocity, particle morphology, and substrate state) on the quality of the Cu-based composite coatings are summarized, and the current research status of cold-sprayed Cu-based composite coatings in the fields of corrosion resistance, wear resistance, self-lubricating properties, and electrical conductivity is reviewed. Moreover, the improvement of the performance of Cu-based composite coatings by various post-process treatments of coatings, such as heat treatment (HT) and friction stir processing (FSP), is elaborated. Finally, the future development of Cu-based composite coatings and CS technology is prospected.
    Type of Medium: Online Resource
    ISSN: 2079-6412
    URL: Article
    DOI: 10.3390/coatings13030479
    Language: English
    Publisher: MDPI AG
    Publication Date: 2023
    detail.hit.zdb_id: 2662314-6
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  • 5
    Online Resource
    Online Resource
    Bending Fatigue Behaviour and Fatigue Endurance Limit Prediction of 20Cr2Ni4A Gear Steel after the Ultrasonic Surface Rolling Process
    MDPI AG ; 2021
    In:  Materials Vol. 14, No. 10 ( 2021-05-12), p. 2516-
    Details
    In: Materials, MDPI AG, Vol. 14, No. 10 ( 2021-05-12), p. 2516-
    Abstract: To study the effect of the surface properties on the bending fatigue performance of heavy-duty gear steel, the authors of this paper used the ultrasonic surface rolling process (USRP) to strengthen 20Cr2Ni4A carburized gear steel. USRP is a novel technique in which the ultrasonic technology is incorporated into the concept of conventional deep rolling. In this study, we illustrated how the surface properties and cross-section mechanical property influence the three-point bending fatigue life of the samples before and after USRP treatment. At the same time, the predicted failure probability-stress-number of cycles (P-S-N) curve was drawn, and the fatigue fracture was analysed. The results show that the fatigue limit increased from 651.36 MPa to 918.88 MPa after USRP treatment. The fatigue source is mainly from the sample interior or surface scratches, and the fatigue performance is positively correlated with the results of the material surface roughness, surface residual stress and surface hardness. At the same time, combined with the change in the phase structure, dislocation structure, residual stress and hardness of the cross section of the material, it is found that the USRP process turns the steel into a gradient material with five layers. Finally, the coupling mechanism between the ultrasonic surface strengthening deformation layer and the carburized layer of 20Cr2Ni4A carburized gear steel is presented, and the grain structure distribution diagram of the section of the 20Cr2Ni4A model after surface strengthening treatment was simulated. The mechanism that influenced the fatigue performance after USRP treatment is explained from the perspectives of the surface and cross section of the samples.
    Type of Medium: Online Resource
    ISSN: 1996-1944
    URL: Article
    DOI: 10.3390/ma14102516
    Language: English
    Publisher: MDPI AG
    Publication Date: 2021
    detail.hit.zdb_id: 2487261-1
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  • 6
    Online Resource
    Online Resource
    Research on Atomic Oxygen Erosion Influence of Structural Damage and Tribological Properties of Mo/MoS2-Pb-PbS Thin Film
    MDPI AG ; 2022
    In:  Materials Vol. 15, No. 5 ( 2022-03-01), p. 1851-
    Details
    In: Materials, MDPI AG, Vol. 15, No. 5 ( 2022-03-01), p. 1851-
    Abstract: To investigate atomic oxygen effects on tribological properties of Mo/MoS2-Pb-PbS film and further enlarge application range, atomic oxygen exposure tests were carried out for 5 h, 10 h, 15 h, and 20 h by the atomic oxygen simulator with atomic oxygen flux of 2.5 × 1015 atoms/cm2·s. The exposure time in test was equivalent to the atomic oxygen cumulative flux for 159.25 h, 318.5 h, 477.75 h, and 637 h at the height of 400 km in space. Then, the vacuum friction test of Mo/MoS2-Pb-PbS thin film was performed under the 6 N load and 100 r/min. By SEM, TEM, and XPS analysis of the surface of the film after atomic oxygen erosion, it was observed that atomic oxygen could cause serious oxidation on the surface of Mo/MoS2-Pb-PbS film, and the contents of MoS2, PbS, and Pb, which were lubricating components, were significantly reduced, and oxides were generated. From AES analysis and the variation in the main element content, Mo/MoS2-Pb-PbS thin film showed self-protection ability in an atomic oxygen environment. Hard oxide generated after atomic oxygen erosion such as MoO3 and Pb3O4 could cause the friction coefficient slight fluctuations, but the average friction coefficient was in a stable state.
    Type of Medium: Online Resource
    ISSN: 1996-1944
    URL: Article
    DOI: 10.3390/ma15051851
    Language: English
    Publisher: MDPI AG
    Publication Date: 2022
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  • 7
    Online Resource
    Online Resource
    Stress Evaluation of Welded Joints with Metal Magnetic Memory Testing Based on Tension–Compression Fatigue Test
    MDPI AG ; 2022
    In:  Materials Vol. 15, No. 9 ( 2022-04-25), p. 3103-
    Details
    In: Materials, MDPI AG, Vol. 15, No. 9 ( 2022-04-25), p. 3103-
    Abstract: Metal magnetic memory testing (MMMT) is an effective nondestructive technique for fatigue damage monitoring of weldments because of its capacity for stress evaluation. An experimental investigation of the effect of the applied fatigue stress on MMMT signals, including the tangential component Bx and the normal component Bz, during tension–compression fatigue tests in welded joints was carried out systematically. The Bx and Bz signals at different fatigue cycles and fatigue stresses were collected and analyzed, and the results showed that there was a peak of Bx and abnormal peaks of Bz that existed at the welded joint before loading. After loading, the peak of Bx and the abnormal peaks of Bz reversed, and the Bx signals moved upward and the Bz signals rotated anticlockwise dramatically in the first few fatigue cycles. After the fatigue cycle number was larger than 1000, Bx and Bz were stable, with very little fluctuation. In addition, the characteristics of Bx signals, the mean value, and the peak value of the average of Bx had an extremely significant linear relationship with the applied fatigue stress during the stable stage of the fatigue test, which indicates that MMMT is a feasible method for fatigue stress evaluation and even residual fatigue life estimation for weldments in service.
    Type of Medium: Online Resource
    ISSN: 1996-1944
    URL: Article
    DOI: 10.3390/ma15093103
    Language: English
    Publisher: MDPI AG
    Publication Date: 2022
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  • 8
    Online Resource
    Online Resource
    Abrasive Wear Resistance of Plasma-Nitrided Ti Enhanced by Ultrasonic Surface Rolling Processing Pre-Treatment
    MDPI AG ; 2019
    In:  Materials Vol. 12, No. 19 ( 2019-10-06), p. 3260-
    Details
    In: Materials, MDPI AG, Vol. 12, No. 19 ( 2019-10-06), p. 3260-
    Abstract: The objective of the given work was to investigate abrasive wear behaviours of titanium (Ti) treated by ultrasonic surface rolling processing (USRP) pre-treatment and plasma nitriding (PN). Simulated lunar regolith particles (SLRPs) were employed as abrasive materials during characterization of tribological performances. The experimental results showed that SLRPs cause severe abrasive wear on Ti plasma-nitrided at 750 °C via the mechanism of micro-cutting. Due to the formation of a harder and thicker nitriding layer, the abrasive wear resistance of the Ti plasma-nitrided at 850 °C was enhanced, and its wear mechanism was mainly fatigue. USRP pre-treatment was effective at enhancing the abrasive wear resistance of plasma-nitrided Ti, due to the enhancement of the hardness and thickness of the nitride layer. Nevertheless, SLRPs significantly decreased the friction coefficient of Ti treated by USRP pre-treatment and PN, because the rolling of small granular abrasives impeded the adhesion of the worn surface. Furthermore, USRP pre-treatment also caused the formation of a dimpled surface with a large number of micropores which can hold wear debris during tribo-tests, and finally, polishing and rolling the wear debris resulted in a low friction coefficient (about 0.5).
    Type of Medium: Online Resource
    ISSN: 1996-1944
    URL: Article
    DOI: 10.3390/ma12193260
    Language: English
    Publisher: MDPI AG
    Publication Date: 2019
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  • 9
    Online Resource
    Online Resource
    Bending Fatigue Behaviors Analysis and Fatigue Life Prediction of 20Cr2Ni4 Gear Steel with Different Stress Concentrations near Non-metallic Inclusions
    MDPI AG ; 2019
    In:  Materials Vol. 12, No. 20 ( 2019-10-21), p. 3443-
    Details
    In: Materials, MDPI AG, Vol. 12, No. 20 ( 2019-10-21), p. 3443-
    Abstract: To investigate the relationship between inclusions and bending fatigue behaviors in 20Cr2Ni4 steel under different stress concentrations. This paper designs a new experimental method to prefabricate different size stress concentrations near the inclusions, and then conducts a new type of bending fatigue test to study the inclusions and their surrounding stress distributions in 20Cr2Ni4 steel. A microhardness tester was combined with laser etching equipment to realize the prefabrication of different stress concentrations at arbitrary positions around any inclusion on the gear steel surface. This method provides an experimental basis for the quantitative analysis of the relationship between stress distribution and fatigue life around the inclusions of heavy-duty gear steels. We also predict the bending fatigue lives of heavy-duty gear steels with different types of inclusions, stress states, and spatial distributions. Then, based on the prefabricated notch parameters and the state of inclusions in the steel, a mathematical model of quantitative analysis is proposed, which can accurately predict the fatigue limit of heavy-duty gear steel. The research results can be applied to the actual use of heavy-duty gears and to the accurate life estimation based on the state of gear stress, thereby providing a quantitative reference model for subsequent gear steel production and gear part processing.
    Type of Medium: Online Resource
    ISSN: 1996-1944
    URL: Article
    DOI: 10.3390/ma12203443
    Language: English
    Publisher: MDPI AG
    Publication Date: 2019
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  • 10
    Online Resource
    Online Resource
    Phase Transition Effect on Ferroelectric Domain Surface Charge Dynamics in BaTiO3 Single Crystal
    MDPI AG ; 2021
    In:  Materials Vol. 14, No. 16 ( 2021-08-09), p. 4463-
    Details
    In: Materials, MDPI AG, Vol. 14, No. 16 ( 2021-08-09), p. 4463-
    Abstract: The ferroelectric domain surface charge dynamics after a cubic-to-tetragonal phase transition on the BaTiO3 single crystal (001) surface was directly measured through scanning probe microscopy. The captured surface potential distribution shows significant changes: the domain structures formed rapidly, but the surface potential on polarized c domain was unstable and reversed its sign after lengthy lapse; the high broad potential barrier burst at the corrugated a-c domain wall and continued to dissipate thereafter. The generation of polarization charges and the migration of surface screening charges in the surrounding environment take the main responsibility in the experiment. Furthermore, the a-c domain wall suffers large topological defects and polarity variation, resulting in domain wall broadening and stress changes. Thus, the a-c domain wall has excess energy and polarization change is inclined to assemble on it. The potential barrier decay with time after exposing to the surrounding environment also gave proof of the surface screening charge migration at surface. Thus, both domain and domain wall characteristics should be taken into account in ferroelectric application.
    Type of Medium: Online Resource
    ISSN: 1996-1944
    URL: Article
    DOI: 10.3390/ma14164463
    Language: English
    Publisher: MDPI AG
    Publication Date: 2021
    detail.hit.zdb_id: 2487261-1
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