Dependence of tungsten melting and resolidification on pulse parameters under transient heat flow
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摘要: 为了研究钨在瞬态热流下达到熔融状态后，不同脉冲参数对其熔融重凝行为的影响，实验观察了钨在脉宽5 ms与0.1 ms的脉冲辐照下熔融重凝行为的特征，并考虑熔融层流动驱动力、冷却速率、温度梯度等多项因素，分析了分层结构与柱状晶对热源参数的依赖性。通过计算两种热源参数下的热作用特性分析了钨在脉宽0.1 ms的脉冲辐照下出现柱状晶而在脉宽5 ms的脉冲辐照下未出现的原因。研究发现，高流强和短脉宽的脉冲束流易于促进形成分层结构，其原因是较高流强能引起材料表层熔化层流动，同时较短脉宽能使熔化层流痕来不及恢复平整，而被快速冷却固化；当样品在瞬态热流下发生熔化时，较短的脉宽有利于形成柱状晶，较长的脉宽有利于形成等轴晶粒和出现晶粒长大。Abstract: To study the influence of different pulse parameters on the melting and resolidification behavior of tungsten after its temperature reaches the melting point under transient heat flow, the differences in morphology and structure of tungsten after melting and resolidification under IPEB (5 ms) and CPF (0.1 ms) were experimentally observed. The dependence of hierarchical structure and columnar crystal grain on pulse parameters was analyzed considering the driving force of molten layer motion, cooling rate, temperature gradient and other factors. The reason why the columnar crystal grains appear on tungsten at pulse width of 0.1 ms but not at pulse width of 5 ms was analyzed by calculating the thermal action characteristics for two heat sources. It is found that the beam with high current intensity and short pulse width is easy to promote the formation of hierarchical structure. The reason is that the high current intensity of the pulse beam can cause the molten layer motion on the surface of the material, while the short pulse width of the pulse beam can make the molten traces too late to recover and be quickly cooled and solidified. When the sample melts under transient heat flow, short pulse width is beneficial to the formation of columnar crystal grains and long pulse width is beneficial to the formation of equiaxed grains and grain growth.
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图 1 钨在脉宽0.1 ms的CPF单脉冲辐照下SEM图及辐照示意图
Figure 1. SEM images and diagram of tungsten under compressed plasma flow (CPF) single pulse irradiation with pulse width of 0.1 ms
图 2 钨在脉宽 0.1 ms的 CPF单脉冲辐照下钨截面的VCD图
Figure 2. VCD diagram of tungsten cross section under CPF single pulse irradiation with pulse width of 0.1 ms
图 3 在能量密度为1.54 MJ/m2 脉宽0.1 ms的 CPF单脉冲辐照下钨表面的液滴和剥离结构的SEM图
Figure 3. SEM images of solidified droplet and stripping structure on tungsten under CPF single pulse irradiation with energy density of 1.54 MJ/m2 and pulse width of 0.1 ms
图 4 钨在能量密度为3.82 MJ/m2 脉宽5 ms的30次IPEB脉冲辐照下SEM图及辐照示意图
Figure 4. SEM images and diagram of tungsten irradiated by 30 IPEB pulses with energy density of 3.82 MJ/m2 and pulse width of 5 ms
图 5 钨在能量密度为3.82 MJ/m2脉宽5 ms的IPEB单脉冲辐照后5 ms时截面温度场分布
Figure 5. The cross-sectional temperature distribution of tungsten at 5 ms after IPEB single pulse irradiation with energy density of 3.82 MJ/m2 and pulse width of 5 ms
图 6 钨在能量密度3.82 MJ/m2、脉宽5 ms的1～10次IPEB脉冲辐照后，表面中心点温度随时间的变化
Figure 6. The evolution of surface temperature with time at the center of irradiation area under 1-10 pulses of IPEB at 3.82 MJ/m2 energy density and 5 ms pulse width
图 7 钨在能量密度3.82 MJ/m2、脉宽5 ms的1～10次IPEB脉冲辐照后，表面温度最高时纵向的温度分布
Figure 7. Distribution of temperature at the center of irradiation area with depth under 1-10 pulses of IPEB at 3.82 MJ/m2 energy density and 5 ms pulse width
表 1 计算的脉宽5 ms与0.1 ms两种脉冲束流辐照钨的热作用特性
Table 1. The calculated thermal characteristics of tungsten irradiated by two kinds of pulse beams with pulse width of 5 ms and 0.1 ms
particle
typeenergy density/
(MJ·m−2)pulse
width/msmelting
time/msmelting layer
thickness/μmIPEB 3.82 5 1.3 60 CPF 1.2 0.1 0.093 32 particle
typetemperature rise
rate/(K·s−1)temperature drop
rate/(K·s−1)maximum axial
temperature gradient/(K·m−1)maximum radial
temperature gradient/(K·m−1)IPEB 5×106 3×106 4×106 5×106 CPF 3×108 6×107 2×108 
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