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摘要: 采用真空感應熔煉法制備了醫用Ti-50. 7%Ni合金(原子數分數), 測試了鑄態合金的成分、相變點、微觀組織和硬度, 并采用Gleeble-3800熱模擬實驗機在變形溫度750~950℃、應變速率0. 001~1 s-1, 應變量為0. 5的條件下對Ni-Ti合金進行高溫壓縮變形, 分析其流動應力變化規律, 建立了高溫塑性變形本構關系和熱加工圖.結果表明: 當變形溫度減小或應變速率增大時, Ni-Ti合金的流動應力會隨之增大.應變速率為1 s-1時, 合金的真應力-真應變曲線呈現出鋸齒狀特征.根據熱加工圖, 獲得了Ni-Ti合金的加工安全區和流變失穩區, 進而確定其合理的熱變形溫度范圍為820~880℃, 真應變速率低于0. 1 s-1.從而為制定鎳鈦合金的鍛造工藝參數提供理論和數據基礎.Abstract: A Ti-50. 7% Ni (atomic fraction) shape alloy was prepared by vacuum induction melting under dynamic argon atmosphere. By analyzing the composition, deformation temperature, microstructure, and hardness of the as-cast Ni-Ti shape alloy in this study, it was found that the properties of the as-cast Ni-Ti alloy met the medical standard. To analyze the variation law of the flow stress, the flow stress of the compression deformation for as-cast Ni-Ti alloy was studied by high-temperature compression with a Gleeble-3800 simulated machine within a deformation temperature range of 750-950 ℃, strain rate range of 0. 001-1. 0 s-1, and strain level of 0. 5. To analyze the relationship between variables in the hot deformation process of as-cast Ni-Ti alloy, a constitutive equation based on dynamic material model was established. To determine the reasonable range of hot working conditions for as-cast Ni-Ti alloy deformation, hot processing maps under different hot deformation conditions were set up. The results show that when the deformation temperature decreases or strain rate increases, the flow stress of as-cast Ni-Ti alloy increases. This phenomenon shows that the main factors affecting the flow stress of as-cast Ni-Ti alloy are deformation temperature and strain rate. When the strain rate is 1. 0 s-1, the true stress-true strain curves of as-cast Ni-Ti alloy exhibits a zigzag feature. This is mainly attributed to the alternation between hardening and softening during deformation. According to the hot processing maps under different hot deformation conditions, the processing zone and unstable hot deformation region of the as-cast Ni-Ti alloy were obtained. Then, the best temperature range of hot deformation is determined as 820-880 ℃, and the true strain rate is less than 0. 1 s-1. This study provides a theoretical and data basis for the development of forging process parameters of Ni-Ti alloy.
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Key words:
- Ni-Ti alloy /
- hot compression /
- strain curves /
- hot processing map
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圖 5 Ni-Ti合金的$\ln \left[ {\sinh \left( {\alpha \sigma } \right)} \right] - \ln \dot \varepsilon $關系曲線(a) 和$\ln \left[ {\sinh \left( {\alpha \sigma } \right)} \right] - {T^{ - 1}}$關系曲線(b)
Figure 5. Relation curve of $\ln \left[ {\sinh \left( {\alpha \sigma } \right)} \right] - \ln \dot \varepsilon $ of Ni-Ti alloy (a) and relation curve of $\ln \left[ {\sinh \left( {\alpha \sigma } \right)} \right] - {T^{ - 1}}$ of Ni-Ti alloy (b)
表 1 本文醫用Ni-Ti合金鑄錠的化學成分(質量分數)
Table 1. Chemical compositions of the medical Ni-Ti alloy in this study
Ni C N H O Ti 55.69 0.069 0.010 0.001 0.045 余量 表 2 DSC法測定的鑄錠相變溫度
Table 2. Ingot phase transition temperature measured by DSC method
馬氏體相變終止溫度,Mf/℃ 馬氏體相變峰值溫度,Mp/℃ 馬氏體相變開始溫度,Ms/℃ 奧氏體相變開始溫度,As/℃ 奧氏體相變峰值溫度,Ap/℃ 奧氏體相變結束溫度,Af/℃ -49 -32 -16 -16 -5 9 表 3 Ni-Ti形狀記憶合金在不同變形條件下的流動應力值
Table 3. Rheological stress and strain values of Ni-Ti alloy under differ-ent deformation conditions
應變量 應變速率/s-1 不同溫度下的流動應力/MPa 750℃ 800℃ 850℃ 900℃ 950℃ 0.1 0.001 85.146 62.551 48.931 42.566 33.268 0.010 146.85 115.86 88.264 72.478 68.129 0.100 243.55 180.24 158.4 127.82 100.34 1.000 326.47 285.74 234.88 203.07 169.07 0.2 0.001 81.899 61.742 48.776 40.358 31.135 0.010 143.9 112.64 85.382 70.403 64.094 0.100 237.88 178.41 157.04 123.73 97.844 1.000 309.36 265.71 228.3 198.52 168.68 0.3 0.001 78.147 60.99 46.518 38.79 29.61 0.010 141.94 108.84 80.703 67.432 59.946 0.100 224.64 178.59 151.53 119.42 92.211 1.000 289.45 253.92 223.79 192.29 163.3 0.4 0.001 76.852 58.794 45.453 37.331 28.22 0.010 134.4 107.74 78.287 67.808 56.722 0.100 214 180.08 150.86 115.87 90.351 1.000 285.38 247.41 223.23 188.73 159.85 259luxu-164 -
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