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1.
Microstructural evolution of AZ31 magnesium alloy welds without and with the addition of titanium powders during resistance
spot welding was studied using optical microscopy, scanning electron microscopy, and transmission electron microscopy (TEM).
The fusion zone of AZ31 magnesium alloy welds could be divided into columnar dendritic zone (CDZ) and equiaxed dendritic zone
(EDZ). The well-developed CDZ in the vicinity of the fusion boundary was clearly restricted and the coarse EDZ in the central
region was efficiently refined by adding titanium powders into the molten pool, compared with the as-received alloy welds.
A microstructural analysis showed that these titanium particles of approximately 8 μm diameter acted as inoculants and promoted
the nucleation of α-Mg grains and the formation of equiaxed dendritic grains during resistance spot welding. Tensile-shear testing was applied
to evaluate the effect of titanium addition on the mechanical properties of welds. It was found that both strength and ductility
of magnesium alloy welds were increased after the titanium addition. A TEM examination showed the existence of an orientation
matching relationship between the added Ti particles and Mg matrix, i.e.,
[ 0 1[`1]0 ]\textMg // [ 1[`2] 1[`3] ]\textTi \textand ( 000 2 )\textMg // ( 10[`1]0)\textTi \left[ {0 1\bar{1}0} \right]_{\text{Mg}} // \, \left[ { 1\bar{2} 1\bar{3}} \right]_{\text{Ti}} \,{\text{and}}\,\left( {000 2} \right)_{\text{Mg}} // \, ( 10\bar{1}0)_{\text{Ti}} in some grains of Ti polycrystal particles. This local crystallographic matching could promote heterogeneous nucleation of
the Mg matrix during welding. The diameter of the added Ti inoculant should be larger than 1.8 μm to make it a potent inoculant. 相似文献
2.
The Au diffusion in the Ti3Al compound was investigated at six compositions from 25 to 35 at. pct Al by using the diffusion couples (Ti-X at. pct Al/Ti-X at. pct Al-2 at. pct Au; X = 25, 27, 29, 31, 32, and 35) at 1273 to 1423 K. The diffusion coefficients of Au in Ti3Al
( D\textAu\textTi3 \textAl ) \left( {D_{\text{Au}}^{{{\text{Ti}}_{3} {\text{Al}}}} } \right) are relatively close to those of Ti. The
D\textAu\textTi3 \textAl \texts {D}_{\text{Au}}^{{{\text{Ti}}_{3} {\text{Al}}}} {\text{s}} slightly increase with Al concentration within the same order of magnitude. The activation energies of Au diffusion,
Q\textAu\textTi3 \textAl \texts, Q_{\text{Au}}^{{{\text{Ti}}_{3} {\text{Al}}}} {\text{s}}, evaluated from the Arrhenius plots were relatively close to those of Ti diffusion,
Q\textTi\textTi3 \textAl \texts, Q_{\text{Ti}}^{{{\text{Ti}}_{3} {\text{Al}}}} {\text{s}}, rather than those of Al diffusion,
Q\textAl\textTi3 \textAl \texts; {Q}_{\text{Al}}^{{{\text{Ti}}_{3} {\text{Al}}}} {\text{s}}; therefore, it was suggested that Au atoms diffuse by the sublattice diffusion mechanism in which Au atoms substitute for
Ti sites preferentially in Ti3Al and diffuse by vacancy mechanism on Ti sublattice. The influence of the D019 ordered structure (hcp base) of Ti3Al on diffusion of Au and other elements is discussed by comparing the diffusivities in Ti3Al and α-Ti. 相似文献
3.
4.
Sound velocity values for 32 liquid metals at their melting point temperatures have been predicted using two models that we
presented; most of these metals are transition and rare earth metals. The sound velocities for most of these liquid metals
have yet to be measured experimentally. Dimensionless common parameters, denoted by
x\textT1/2 \xi_{\text{T}}^{1/2} and
x\textE1/2 , \xi_{\text{E}}^{1/2} , were determined on the basis of the predicted sound velocities. These common parameters, which characterize the liquid state
(i.e., an atom’s hardness or softness and its anharmonic motions), allow for better predictions of several thermophysical properties
(e.g., surface tension, viscosity, self-diffusivity, volume expansivity) of liquid metallic elements. The values of both the common
parameters
x\textT1/2 \xi_{\text{T}}^{1/2} and
x\textE1/2 \xi_{\text{E}}^{1/2} vary periodically with atomic number. Using our viscosity model in terms of the parameter
x\textT1/2 , \xi_{\text{T}}^{1/2} , values of melting point viscosity were calculated for liquid molybdenum and platinum. The agreement obtained between calculated
and experimental values is good when using predicted values of
x\textT1/2 \xi_{\text{T}}^{1/2} to calculate their viscosities. 相似文献
5.
Chang-Woo Seo Seon-Hyo Kim Sung-Koo Jo Min-Oh Suk Sun-Min Byun 《Metallurgical and Materials Transactions B》2010,41(4):790-797
High-melting-point inclusions such as spinel(Al2O3·xMgO) are known to promote clogging of the submerged entry nozzle (SEN) in a continuous caster mold. In particular, Ti-alloyed
steels can have severe nozzle clogging problems, which are detrimental to the slab surface quality. In this work, the thermodynamic
role of Ti in steels and the effect of Ca and Ti addition to the molten austenitic stainless steel deoxidized with Al on the
formation of Al2O3·xMgO spinel inclusions were investigated. The sequence of Ca and Ti additions after Al deoxidation was also investigated. The
inclusion chemistry and morphology according to the order of Ca and Ti are discussed from the standpoint of spinel formation.
The thermodynamic interaction parameter of Mg with respect to the Ti alloying element was determined. The element of Ti in
steels could contribute to enhancing the spinel formation, because Ti accelerates Mg dissolution from the MgO containing refractory
walls or slags because of its high thermodynamic affinity for Mg
( e\textMg\textTi = - 0. 9 3 3). ( {e_{\text{Mg}}^{\text{Ti}} = - 0. 9 3 3}). Even though Ti also induces Ca dissolution from the CaO-containing refractory walls or slags because of its thermodynamic
affinity for Ca
( e\textCa\textTi = - 0.119 ), \left( {e_{\text{Ca}}^{\text{Ti}} = - 0.119} \right), dissolved Ca plays a role in favoring the formation of calcium aluminate inclusions, which are more stable thermodynamically
in an Al-deoxidized steel. The inclusion content of steel samples was analyzed to improve the understanding of fundamentals
of Al2O3·xMgO spinel inclusion formation. The optimum processing conditions for Ca treatment and Ti addition in austenitic stainless
steel melts to achieve the minimized spinel formation and the maximized Ti-alloying yield is discussed. 相似文献
6.
Shoko Komiyama Yuji Sutou Junichi Koike 《Metallurgical and Materials Transactions A》2011,42(11):3310-3315
Effects of nitrogen content on the microstructure, hardness, and friction coefficient of Ti-Mo-N coating films were investigated.
Ti-Mo-N films were deposited onto an AISI304 stainless steel substrate by reactive r.f. sputtering in the mixture of argon
and nitrogen gases with various gas flow rates. The hardness and friction coefficients were measured by nanoindentation and
ball-on-disk testing systems, respectively. The hardness of the Ti-Mo-N films increased with increasing a nitrogen gas flow
rate
( f\textN2 ) \left( {f_{{{\text{N}}_{2} }} } \right) and showed a maximum hardness of about 30 GPa at a
f\textN2 = 0.3 \textccm f_{{{\text{N}}_{2} }} = 0.3\,{\text{ccm}} . On the one hand, the films deposited at
f\textN2 3 1.0 \textccm f_{{{\text{N}}_{2} }} \ge 1.0\;{\text{ccm}} showed a constant hardness value of approximately 25 GPa. On the other hand, the friction coefficient of the Ti-Mo-N film
decreased with increasing N content and was 0.44 in the film deposited at
f\textN2 = 2.0 \textccm. f_{{{\text{N}}_{2} }} = 2.0\;{\text{ccm}}. 相似文献
7.
Martin Selin 《Metallurgical and Materials Transactions A》2010,41(11):2805-2815
A comparison between three constituent relationships used to approximate the plastic part of a tensile test curve was performed
on compacted graphite cast iron (CGI) samples at temperatures between room temperature and 873 K (600 °C). The investigated
relationships were the Hollomon, Ludwigson, and Voce equations. The investigated CGI materials were alloyed with four different
amounts of molybdenum, and each chemical composition was cast with three different solidification rates. The two coefficients
in the Hollomon equation
s\textH = K\textH ×en\textH \sigma_{\text{H}} = K_{\text{H}} \times \varepsilon^{{n_{\text{H}} }} showed a temperature dependence, where the strength coefficient K
H was temperature stable for temperatures up to 573 K (300 °C) and the strain-hardening exponent n
H showed a maximum value at about 473 K (200 °C). Both coefficients were affected by an altered metal matrix and by increased
nodularity, and they showed a slight increased value with reduced pearlite interlamellar spacing. Ludwigson added an exponential
term
eK\textL + n\textL ×e , e^{{K_{\text{L}} + n_{\text{L}} \times \varepsilon }} , including two new coefficients to the Hollomon equation, to adjust and improve the approximation. The main purpose of K
L was to adjust the stress value at zero plastic strain and was affected little by the metal matrix constituents and microstructure
features. The value of n
L was greatly dependent on the total plastic strain in which small plastic strains resulted in larger n
L values, whereas large plastic strains resulted in smaller values. The deformation behavior was similar for all samples; hence,
the total plastic strain also had a large influence on whether the adjustment term was positive or negative as a consequence
of how n
H was chosen. Compared with the Hollomon and Ludwigson equations, the Voce equation
s\textV = sS - ( sS - s1 )en\textV ×e \sigma_{\text{V}} = \sigma_{S} - \left( {\sigma_{S} - \sigma_{1} } \right)e^{{n_{\text{V}} \times \varepsilon }} included coefficients representing an initial stress value σ
1 and a saturation stress value σ
S
. The initial stress values and the saturation stress values showed great linear correlations with yield strength values at
0.2 pct elongation and ultimate tensile strength, respectively. The values of both these coefficients were reduced with increasing
temperature but had a plateau or even a slight increase between about 473 K and 573 K (200 °C and 300 °C). n
V was reduced constantly with increasing temperature and was affected by the total plastic strain values in the same way as
n
L. The overall best approximation of the stress values was made by the Ludwigson equation followed by the Hollomon equation
and last by the Voce equation. The downside with the Ludwigson equation was that the correction term either could be positive
or negative, which made it harder to use as a general equation to approximate stress values, compared with the Hollomon and
Voce equations. 相似文献
8.
To derive a correlation between sulfide and chloride capacities through our own systematic experimental studies by using a
gas equilibrium technique involving Ar-H2-H2O-HCl gas mixtures, the solubilities of chlorine were determined for CaO-SiO2-MgO-Al2O3 slags at temperatures between 1673 K and 1823 K (1400 °C and 1550 °C). As a formula to correlate sulfide and chloride capacities,
the following equation that is the function of temperature only was obtainable;
2logC\textCl - logC\textS = - 64.4 + \frac82,890T(\textK) ±0.75 2\log C_{\text{Cl}} - \log C_{\text{S}} = - 64.4 + {\frac{82,890}{{T({\text{K}})}}} \pm 0.75 相似文献
9.
Takashi Nagai Yusuke Tanaka Masafumi Maeda 《Metallurgical and Materials Transactions B》2011,42(4):685-691
The thermodynamic properties of the CaO-P2O5 system are important to develop an effective refining process in the iron and steel industry. In this study, the thermodynamic
properties of (CaO)2P2O5 were investigated because the properties are necessary to develop a new dephosphorization process. The vapor of gaseous phosphorus
and phosphorus oxide in equilibrium with a mixture of (CaO)2P2O5 and (CaO)3P2O5 at 1373 K to 1498 K (1100 °C to 1225 °C) were detected directly as an ion current by double Knudsen cell mass spectrometry.
Comparing the ion currents with those from a mixture of Al2O3P2O5 and Al2O3, which is used as a reference mixture in this study, the Gibbs energy change of the following reaction was calculated:
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