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1.
A three-dimensional model of the spray forming method 总被引:2,自引:0,他引:2
Hyun-Kwang Seok Kyu Hwan Oh Hyung Yong Ra Dong-Hun Yeo Ho-In Lee 《Metallurgical and Materials Transactions B》1998,29(3):699-708
A three-dimensional model has been formulated to calculate the shape of the general preform, using vector calculus. The shape
of a rod, tube, plate, or irregular preform can be calculated at given spray forming conditions. The shape of a spray-formed
rod was analyzed at various spray forming conditions using the three-dimensional model. The effects of spray forming parameters,
such as spray distribution parameters, angular velocity of rotation, withdrawal velocity, spray angle, and eccentric distance
on rod shape, were analyzed. The most important parameters affecting the shape of rods are the spray distribution parameters
and the withdrawal velocity. The dynamic evolution of rod shape with a stepwise variation of the withdrawal velocity during
spray forming was investigated. The effect of a stepwise change of the withdrawal velocity was the same as that of the scanning
atomizer. The calculated surface profiles were compared with those of spray-formed 7075 aluminum alloy rods prepared on a
pilot scale. The calculated results for the surface profiles were in agreement with those of the spray-formed rods. 相似文献
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Modeling of spray-formed materials: Geometrical considerations 总被引:3,自引:0,他引:3
Y. J. Lin E. J. Lavernia J. E. Bobrow D. R. White 《Metallurgical and Materials Transactions A》2000,31(11):2917-2929
In this article, a mathematical model is formulated to predict the evolution and final geometry of an axisymmetric billet
(i.e., round) obtained using an off-axis spray arrangement. The model is formulated by calculating the shape change of a profile
curve of a billet surface, based on an axisymmetric surface. On the basis of this model, a methodology to determine the “shadowing
effect” coefficient is presented. The modeling results suggest that there are three distinct regions in a spray-formed billet:
a base transition region, a uniform diameter region, and an upper transition region. The effects of several important processing
parameters, such as the withdrawal velocity of substrate, maximum deposition rate, spray distribution coefficient, initial
eccentric distance, and rotational velocity of substrate, on the shape factors (e.g., the diameter size of the uniform region and the geometry of the transition regions) are investigated. The mechanisms responsible
for the formation of the three distinct regions are discussed. Finally, the model is then implemented and a methodology is
formulated to establish optimal processing parameters during spray forming, paying particular attention to deposition efficiency. 相似文献
5.
《Acta Metallurgica Materialia》1993,41(11):3109-3118
A computer model has been developed to describe the in-flight dynamic and thermal histories of gas atomised droplets as a function of distance during spray forming. The model has been used to investigate the effects of the dynamic and thermal behaviour of individual gas atomised droplets and the cooling and solidification behaviour of the overall spray. The most influential parameters for a given alloy system, in order of importance, are: (i) droplet diameter and, therefore, the droplet size distribution within the spray; (ii) initial axial gas velocity at the point of atomisation and the subsequent gas velocity decay profile; (iii) melt mass flow rate; (iv) melt superheat at the point of atomisation; and (v) alloy composition. Experimental measurements of gas velocities and droplet size distributions during spray forming allow the spray solid fraction at deposition to be calculated and used in a subsequent computer model of billet heat flow to predict the billet top surface temperatures and solid fractions. 相似文献
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Analysis on the deposition behavior of spray on deposition surface was made and an optimization method for the movement parameters (u, ω) of substrate was obtained. Simultaneously, a mathematical model of growth of tubular preform, specifically aimed at the kind of atomizer that is fixed and with a tilt angle was established. By integrating the optimization method and the mathematical model, the growth process and shape of preform were simulated. The results show that the tilt angle of atomizer plays an important role on the dimensions and shapes of tubular preforms and it can provide a guidance for the development of spray forming equipment. 相似文献
8.
Evolution of microstructure and texture in Mg-Al-Zn alloys during electron-beam and gas tungsten arc welding 总被引:3,自引:0,他引:3
The evolution of microstructure and texture in the AZ-series Mg alloys subjected to electron-beam welding and gas tungsten
arc welding are examined. Electron-beam welding is demonstrated to be a promising means of welding delicate Mg plates, bars,
or tubes with a thickness of up to 50 mm; gas tungsten arc welding is limited to lower-end thin Mg sheets. The grains in the
fusion zone (FZ) are nearly equiaxed in shape and ∼8 μm or less in size, due to the rapid cooling rate. The as-welded FZ microhardness and tensile strength are higher than the
base metals due to the smaller grain size. The weld efficiency, defined as the postweld microhardness or tensile strength
at the mid-FZ region divided by that of the unwelded base metal, is around 110 to 125 pct for electron-beam welding and 97
to 110 pct for gas tungsten arc welding. There are three main texture components present in the electron-beam-welded (EBW)
FZ, i.e.,
(with TD//
),
(with ND∧
∼15 deg), and
(with WD∧
∼30 deg), where TD, ND, and WD are the transverse, normal, and welding directions, respectively. The crystal growth tends
to align toward the most closed-packed direction,
. The texture in gas tungsten arc welded (GTAW) specimens is more diverse and complicated than the EBW counterparts, due to
the limited and shallow FZ and the lower cooling rate. The cooling rates calculated by the three-dimensional (3-D) and two-dimensional
(2-D) heat-transfer models are considered to be the lower and upper bounds. The cooling rate increases with decreasing Al
content, increasing weld speed, and increasing distance from the weld top surface. The influences of the FZ location, welding
speed, and alloy content on the resulting texture components are rationalized and discussed. 相似文献
9.
《Acta Metallurgica》1989,37(2):429-443
Net or near net shape products can be manufactured by technologies involving solidification processing, metal forming, paniculate processing, and droplet consolidation. One example of droplet consolidation is spray deposition in the Ospreytm mode. In this process, a stream of liquid metal is atomized by an inert gas to form a spray of molten droplets; these are accelerated towards a substrate where they impinge and consolidate. An integral model for the Ospreytm spray deposition process has been developed using established theoretical principles. Mathematical models describe the interconnected processes of droplet-gas interactions in flight and subsequent droplet consolidation on the substrate. The models predict droplet velocity and temperature as a function of flight distance, the extent of droplet solidification on arrival at the substrate, and temperature distribution in the consolidated material during deposition. This approach demonstrates the utility of modeling studies in order to establish quantitative guidelines for optimization of the process in terms of the evolution of microstructure in droplet consolidation. 相似文献
10.
Recrystallization kinetics in a (111)[1
0] iron single crystal deformed 70 pet by rolling were characterized experimentally at temperatures between 500°C and 600°C
by means of quantitative metallography. A Laplace transform method was applied to the time-dependent global microstructural
properties, volume fraction, interface area per unit volume, and the largest intercept-free length (recrystallized grain)
to separate nucleation and interface migration effects from the overall recrystallization kinetics. A comprehensive nucleation
and growth model was derived from analysis of the microstructural data. The model consisted of the following salient features:
(a) nucleation was random and approximately site-saturated with zero incubation time at all temperatures; (b) the recrystallized
grains grew three-dimensionally in the shape of prolate spheroids; and (c) interface migration rates were highly anisotropic,
the grains growing at an approximately constant rate in one dimension and at a strongly decreasing rate in the other two dimensions.
The present findings were compared to a similar earlier study of a deformed iron (111)[
2] single crystal. The time dependencies of the interface migration rates were rationalized in terms of a deformation-induced,
nonuniform distribution of stored energy and an orientation-dependent grain boundary mobility. 相似文献
11.
A mathematical, two-dimensional model for the analysis of the temperature and solidification behaviour in the substrate and deposit for the spray forming process of metals has been developed. Due to the irregular shape of the growing deposit, which changes with spraying time, a grid transformation method was successfully developed for the calculation of the temperature distribution and solidification front in the growing deposit. The influence of process parameters, i.e. thermal conditions of the metal spray at impact, heat transfer coefficient at the surface of the deposit and geometrical parameters, are qualitatively and quantitatively discussed. 相似文献
12.
Rong-Jiunn Su Ruel A. Overfelt Wartan A. Jemian 《Metallurgical and Materials Transactions A》1998,29(9):2375-2381
The transient behavior of mushy-zone velocities, primary dendrite arm spacings, and microsegregation effects have been investigated
for an Al-4.5 wt pct Cu alloy by instantaneous velocity changes in a standard Bridgman furnace. After suddenly imposed velocity
changes, the mushy-zone velocities, dendrite arm spacings, and compositions exponentially adjust to new steady-state values.
Good agreement was found between the transient mushy-zone positions and velocities and predictions from the theoretical model
of Saitou and Hirata. The primary dendrite arm spacings appear to adjust to changed velocity conditions about as rapidly as
the mushy-zone velocity adjusts. Steady-state arm spacings agree very well with corresponding steady-state data from the literature.
However, the observed composition profiles in the dendrite core and the interdendritic liquid appear to adjust more slowly
than the corresponding adjustment of the mushy-zone velocity and arm spacings. Our observation of the sluggish response of
the compositional profiles is consistent with an estimated Lewis number
of 9.4 × 103 for the aluminum-copper system. The diffusivity of heat, thus, greatly exceeds the diffusivity of solute in this system.
These results indicate that testing for the steady state during directional solidification experiments by looking for constant
primary dendrite arm spacings can lead to errors, since the microsegregation profiles adjust more slowly than the spacings.
It is suggested that constancy of composition also be tested for critical experiments investigating steady-state microsegregation
effects. 相似文献
13.
REN Sanbing FAN Junfei LE Hairong Advanced Technology Division Research Institute Baoshan Iron & Steel Co. Ltd. Shanghai China 《Baosteel Technical Research》2011,5(3):15-19
Spray forming is a new type of metal material forming process,which can produce metal blanks such as billet,tube,plate etc.A mathematical model has been developed to forecast the shape evolution of tube billets during the spray forming process.The atomizer mass flux as,radial distribution coefficient bs,draw velocity and diameter of mandrel were considered in this model and the influence of different parameters such as metal flowrate,draw velocity of mandrel,diameter of mandrel on the tube’s shape change were simulated and analyzed in this paper.The simulation results obtained from this model can be provided to engineers as reference. 相似文献
14.
H. S. Ryoo S. K. Hwang B. K. Kim H. S. Chung 《Metallurgical and Materials Transactions A》2000,31(8):1925-1935
The process of triangular prism formation and abnormal grain growth of WC was modeled using pseudo-Monte-Carlo simulation
based on atomic adsorption and the coalescence mechanism. Grains of WC evolved into a triangular prism shape due to {10
0} and {1
10} planes of fast growth rate. Coalescence of {10
0} and {1
00} planes subsequent to the anisotropic evolution was the main reason for the abnormal grain growth. The probability of coalescence
computed by the Monte-Carlo method agreed well with a theoretical prediction. Experimental evaluation of the computational
model was made in sintered WC-25 wt pct Co alloy. The experimental alloy was made with WC powder of different particle size,
0.8 μm and −325 mesh, respectively, and with two different sintering conditions: solid-phase sintering and liquid-phase sintering.
The sample made from the coarse powder (−325 mesh) showed the same morphological characteristics as those of the original
milled state, whereas the sample made from the fine powder (0.8 μm) assumed a triangular prism shape quickly during solid-phase sintering. The anisotropic growth process of the latter sample
could be explained by using the adsorption and coalescence model. 相似文献
15.
Y. J. Lin W. Feng J. E. Bobrow E. J. Lavernia 《Metallurgical and Materials Transactions A》2001,32(13):831-840
A mathematical model, incorporating the thermal component of sticking efficiency (SE
t) into the calculation of shape evolution, is formulated to predict the evolution and final geometry of plates. The plates
are spray formed using a moving substrate displaced in a two-dimensional (i.e., X-Y) plane. By using this model, the effects of the substrate movement parameters, such as the acceleration, time required to
complete a stroke in the reciprocal movement direction (X-axis), and the velocity in the uniform movement direction (Y-axis), on the shapes of the plates are investigated. The processing parameters are evaluated by minimizing the values of
the mean-squared (MS) surface roughness. On the basis of the evaluation, the optimal combinations of processing parameters are found. 相似文献
16.
Y.J Lin E. J. Lavernia J. E. Bobrow W. Feng 《Metallurgical and Materials Transactions A》2001,32(3):831-840
A mathematical model, incorporating the thermal component of sticking efficiency (SE
t) into the calculation of shape evolution, is formulated to predict the evolution and final geometry of plates. The plates
are spray formed using a moving substrate displaced in a two-dimensional (i.e., X-Y) plane. By using this model, the effects of the substrate movement parameters, such as the acceleration, time required to
complete a stroke in the reciprocal movement direction (X-axis), and the velocity in the uniform movement direction (Y-axis), on the shapes of the plates are investigated. The processing parameters are evaluated by minimizing the values of
the mean-squared (MS) surface roughness. On the basis of the evaluation, the optimal combinations of processing parameters are found. 相似文献
17.
G. Zhang Z. Li Y. Zhang J. Mi P. S. Grant 《Metallurgical and Materials Transactions B》2010,41(2):303-307
A numerical study of the deposition dynamics of twin-atomizer spray-forming of large-diameter billets is presented with a
focus on the coupled effect of the twin-atomizer scan frequency and substrate rotation frequency. The common period of the
two frequencies ξ was the dominant parameter to govern the deposited droplet mass and billet shape. When ξ ≥ 10, a uniform
mass distribution at the deposition surface was predicted, and the calculated shape agreed with experiments. 相似文献
18.
A simple, but comprehensive model of heat transfer and solidification of the continuous casting of steel slabs is described,
including phenomena in the mold and spray regions. The model includes a one-dimensional (1-D) transient finite-difference
calculation of heat conduction within the solidifying steel shell coupled with two-dimensional (2-D) steady-state heat conduction
within the mold wall. The model features a detailed treatment of the interfacial gap between the shell and mold, including
mass and momentum balances on the solid and liquid interfacial slag layers, and the effect of oscillation marks. The model
predicts the shell thickness, temperature distributions in the mold and shell, thickness of the resolidified and liquid powder
layers, heat-flux profiles down the wide and narrow faces, mold water temperature rise, ideal taper of the mold walls, and
other related phenomena. The important effect of the nonuniform distribution of superheat is incorporated using the results
from previous three-dimensional (3-D) turbulent fluid-flow calculations within the liquid pool. The FORTRAN program CONID
has a user-friendly interface and executes in less than 1 minute on a personal computer. Calibration of the model with several
different experimental measurements on operating slab casters is presented along with several example applications. In particular,
the model demonstrates that the increase in heat flux throughout the mold at higher casting speeds is caused by two combined
effects: a thinner interfacial gap near the top of the mold and a thinner shell toward the bottom. This modeling tool can
be applied to a wide range of practical problems in continuous casters. 相似文献
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20.
A thermal model of laser cladding by powder injection 总被引:10,自引:0,他引:10
A two-dimensional (2-D) finite element model is presented for laser cladding by powder injection. The model simulates the
quasi-steady temperature field for the longitudinal section of a clad track. It takes into account the melting of the powder
in the liquid pool and the liquid/ gas free surface shape and position, which must conform to the thermal field in order to
obtain a self-consistent solution. The results for an idealized problem, where there is almost no melting of the substrate
material, demonstrate the linear relationship between the laser power, the processing velocity, and the thickness of the deposited
layer. The calculated clad heights agreed well with the experimental values for the conditions where a cobalt-based hard-facing
alloy is clad onto mild steel with a linearly focused laser source.
Formerly Postdoctoral Fellow, Ecole Polytechnique Fédérale de Lausanne 相似文献