| 1. |
- Cao, Yu, 1969, et al.
(author)
-
Mechanical Behaviour of a Rephosphorized Steel for Car Body Applications — Effects of Temperature, Strain Rate and Pre-treatment
- 2011
-
In: Journal of Engineering Materials and Technology, Transactions of the ASME. - : ASME International. - 1528-8889 .- 0094-4289. ; 133:2, s. 021019-1 - 021019-11-
-
Journal article (peer-reviewed)abstract
- Temperature and strain rate effects on the mechanical behaviour of a commercial rephosphorized, interstitial free steel have been investigated by uniaxial tensile testing, covering applicable temperatures (-60 – +100°C) and strain rates (1•10-4 – 1•102 s-1) experienced in automotive crash situations. The effect of prestraining to 3.5 % with or without successive annealing at 180°C for 30 min has also been evaluated. These treatments were used to simulate pressing of the plates and the paint-bake cycle in the production of car bodies. Yield and ultimate tensile strengths, ductility including uniform and total elongation and area reduction, thermal softening effect at high strain rate and strain rate sensitivity of stress were determined and discussed in all cases. It was found that the Voce equation [σ = σs- (σs -σ0) exp (ε/ε0)] can be fitted to the experimental true stress-true plastic strain data with good precision. The parameter values in this equation were evaluated and discussed. Furthermore, temperature and strain rate effects were examined in terms of thermal and athermal components of the flow stresses. Finally, a thermal activation analysis was performed.
|
|
| 2. |
- Cao, Yu, 1969, et al.
(author)
-
Temperature and strain rate effects on the mechanical behavior of dual phase steel
- 2015
-
In: Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing. - : Elsevier BV. - 0921-5093. ; 636, s. 124-132
-
Journal article (peer-reviewed)abstract
- The effect of temperature and strain rate on the mechanical behavior of a commercial dual phase steel (DP 800) has been investigated experimentally by uniaxial tensile tests in this study, covering temperatures (−60 °C to 100 °C) and strain rates (1×10–4 to 1×10+2 s−1) encompassing conditions experienced in automotive crash situations. Yield and ultimate tensile strength, ductility, temperature effects and strain rate sensitivity have been determined and discussed. It was found that the Voce equation [σ=σs−(σs−σ0)exp(−εθ0/σs))] can be satisfactorily applied to describe the tensile flow curves by means of a modified Kocks–Mecking model. In this model the parameter θ0 is fixed, whereas both σ0 and σs consist of athermal and thermal stress components. The athermal component is only weakly dependent on temperature through the elastic shear modulus μ. The thermal stress component is governed by temperature and strain rate. Statistical analysis based on the experimental data has allowed all parameters in the Voce equation to be quantified.
|
|
| 3. |
- Cao, Yu, 1969, et al.
(author)
-
The influence of temperatures and strain rates on the mechanical behavior of dual phase steel in different conditions
- 2015
-
In: Journal of Materials Research and Technology. - : Elsevier BV. - 2238-7854 .- 2214-0697. ; 4:1, s. 68-74
-
Journal article (peer-reviewed)abstract
- This study deals with the mechanical behavior of DP steel. A commercial dual phase steel (DP 800) was strained to 3.5% followed by annealing at 180 degrees C for 30 min to simulate the pressing of the plates and the paint bake cycle involved in the manufacturing process of automobile body structures. The effect of temperarure and strain rate on the machanical behavior of this material was investigated by uniaxial tensile tests, covering applicable temperatures (-60 degree C to +100 degree C) and strain rates (1x10exp-4 s-1 to 1x10exp+2 s-1) experienced in automotive crash situations. Yield and ultimate tensile strength, ductility, temperature effects and strain rate sensitivity as well as strain rate hardening rate have been determined and discussed.
|
|
| 4. |
- Liu, Lihui, 1985, et al.
(author)
-
Substrate-dependent resistance decrease of graphene by ultraviolet-ozone charge doping
- 2016
-
In: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 6:67, s. 62091-62098
-
Journal article (peer-reviewed)abstract
- Large sheet resistance is the critical problem of graphene for application in electronic and optoelectronic devices as transparent electrodes. Ultraviolet/ozone (UVO) treatment is a convenient, highly effective, vacuum process and post-clean free method. This paper reveals that the effect of UVO treatment on the resistance of graphene is substrate dependent, which means that the band gap and photogenerated charge carriers of the substrates under UV illumination play a key role in the doping effect. The resistance of graphene can be decreased by as much as 80% on F8BT, GaN and PTFE substrates, by 70% on PMMA substrate, and by 50% on paraffin and glass substrates. Large band gap substrates (>hν) will induce a p-doping effect, while small band gap substrates (
|
|
| 5. |
- Nagaram, Anok Babu, 1987, et al.
(author)
-
Full Density Powder Metallurgical Cold Work Tool Steel through Nitrogen Sintering and Capsule-Free Hot Isostatic Pressing
- 2024
-
In: Metals. - : Multidisciplinary Digital Publishing Institute (MDPI). - 2075-4701. ; 14:8
-
Journal article (peer-reviewed)abstract
- Vanadis 4E (V4E) is a powder metallurgical cold work tool steel predominantly used in application with demand for wear resistance, high hardness, and toughness. It is of interest to have a processing route that enables full density starting from clean gas-atomized powder allowing component shaping capabilities. This study presents a process involving freeze granulation of powder to facilitate compaction by means of cold isostatic pressing, followed by sintering to allow for capsule-free hot isostatic pressing (HIP) and subsequent heat treatments of fully densified specimens. The sintering stage has been studied in particular, and it is shown how sintering in pure nitrogen at 1150 °C results in predominantly closed porosity, while sintering at 1200 °C gives near full density. Microstructural investigation shows that vanadium-rich carbonitride (MX) is formed as a result of the nitrogen uptake during sintering, with coarser appearance for the higher temperature. Nearly complete densification, approximately 7.80 ± 0.01 g/cm3, was achieved after sintering at 1200 °C, and after sintering at 1150 °C, followed by capsule-free HIP, hardening, and tempering. Irrespective of processing once the MX is formed, the nitrogen is locked into this phase and the austenite is stabilised, which means any tempering tends to result in a mixture of austenite and tempered martensite, the former being predominate during the sequential tempering, whereas martensite formation during cooling from austenitization temperatures becomes limited.
|
|
| 6. |
- Wei, Xiuyu, 1979, et al.
(author)
-
Corrosion Behavior of WC-Co-(Ni)-(Cr) Cemented Carbide in Neutral Solution
- 2020
-
In: Xiyou Jinshu Cailiao Yu Gongcheng/Rare Metal Materials and Engineering. - 1002-185X. ; 49:1, s. 313-319
-
Journal article (peer-reviewed)abstract
- Three groups of WC-Co-(Ni)-(Cr) cemented carbides with different binder phase compositions were prepared by powder metallurgy using WC, Co, Ni and Cr3C2 powders as raw materials. The corrosion behavior of the three alloys in neutral solution was studied by polarization curve test and immersion experiment. The corrosion mechanism was discussed by means of scanning electron microscopy, energy spectrum analysis, X-ray photoelectron spectroscopy (XPS) and EBSD. The results show that in neutral solution the corrosion of WC-Co and WC-Co-Cr cemented carbides is mainly caused by the selective dissolution of Co and the corrosion products after immersion are mainly composed of Co(OH)2. The corrosion resistance of WC-Co cemented carbide in neutral solution can be improved by the addition of Cr, which may be related to the decrease in the content of hcp-Co in the binder phase by adding Cr. Adding Ni and Cr together can further improve the corrosion resistance of WC-Co cemented carbide in neutral solution. After immersion for 480 h in Na2SO4 solution, the WC-Co-Ni-Cr alloy sample is just corroded slightly.
|
|
| 7. |
|
|
| 8. |
- Bojestig, Eric, 1991, et al.
(author)
-
Surface chemical analysis of copper powder used in additive manufacturing
- 2020
-
In: Surface and Interface Analysis. - : Wiley. - 1096-9918 .- 0142-2421. ; 52:12, s. 1104-1110
-
Journal article (peer-reviewed)abstract
- Additive manufacturing (AM) has during years gained significant interest owing to its endless component design possibilities. One of the most popular AM techniques is laser powder bed fusion (LPBF), which selectively melts metal powder layer-by-layer in a chamber with protective argon atmosphere. This technique is attractive for realizing Cu-based products in which the high electrical conductivity of Cu is combined with component design possibilities. The successful use of Cu powder not only poses challenges owing to the high reflectivity and thermal conductivity of Cu but also involves the important concern of controlling the powder surface chemistry since the powder surface constitutes the main source of oxygen. It is of crucial importance to control the oxygen level in order to maintain good electrical conductivity and brazing ability of the AM-fabricated Cu-part. In LPBF, fine spherical powder with size of 10-60 mu m is used, providing significant specific surface area, and this powder is also usually recycled several times, and hence, the role of powder surface chemistry is evident. Two kinds of copper powder with purities 99.70 and 99.95 wt% were analysed in both virgin and in used conditions after numerous printing cycles using LPBF. The powder was analysed by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). A clear difference between the two powder grades in terms of surface chemistry was observed. The oxide thickness and bulk oxygen content increased for both powder grades after recycling. The surface oxides under different conditions are identified and the effect of powder purity on the oxide formed is discussed.
|
|
| 9. |
|
|
| 10. |
- Cao, Yu, 1969, et al.
(author)
-
Contact Formation on Silicon Carbide by Use of Nickel and Tantalum in a Materials Science Point of View
- 2011
-
In: Properties and applications of silicon carbide. - 9789533072012 ; , s. 171-194
-
Book chapter (other academic/artistic)abstract
- The advantageous electrical, thermal and mechanical properties make silicon carbide (SiC) a promising semiconductor for high temperature, high power and high frequency applications. Nickel (Ni) and tantalum (Ta) can be used to form both ohmic and Schottky contact. Since metallization represents one of the most important steps in the fabrication of electronic devices, the knowledge of the interaction between Ni, Ta and SiC are of primary importance for understanding and optimising the device performance. In this chapter, an introduction of thermodynamics in Ni (or Ta)-Si-C system is given. The reaction process and mechanisms of Ni-SiC during annealing are reviewed. The phases existing in the film or at the interface and the distribution of elements in-depth are clarified. The impact of pre-treatment on SiC substrate and Ni layer thickness on phase distribution is summarized. The nature of the thermally induced solid-state reactions between Ta or Ni/Ta bilayer and SiC substrate over a wide temperature range is also discussed.
|
|
