论文总字数：20968字

摘 要

钛合金具有密度小、比强度高、弹性模量小、无磁性、耐腐蚀、高温蠕变性能好等特点，被广泛地应用于生物医疗、石油化工、航空航天等领域，其性能优势也日益显著。但钛合金也存在一些缺陷，其在低温下的塑性较差，加工生产工艺复杂，周期长，成材率低，生产过程中产生大量的残料，进一步增加了其使用成本。因此，成本问题成为限制钛合金广泛应用的另一个重要因素。细晶强化是提高金属材料强度和性能的重要方式之一，等通道转角挤压（Equal Channel Angular Pressing，简称ECAP）技术，作为一种新型塑性加工方法，可以在不改变材料尺寸的前提下使试样发生剧烈塑性变形（Severe Plastic Deformation,简称：SPD），通过累积大量应变，降低晶粒尺寸，从而有效细化晶粒，改善组织及成分分布，大幅度提高材料的强度及综合力学性能，也能避免合金元素的添加带来的冶金缺陷和成本问题。一般的材料经过加工之后都会产生例如位错缠结、应力集中等的晶体缺陷，对金属材料进行热处理能够有效消除生产加工过程中产生的晶体缺陷，从而改善材料的性能。对传统的粗晶材料而言，退火处理会使材料的强度降低。然而，对超细晶钛合金进行低温短时退火处理，不但不会降低材料的强度，反而会有效抑制材料晶粒的长大，导致超细晶钛合金的异常硬化，使其性能更加优异。

本课题主要研究低温短时退火对ECAP制备的超细晶钛合金Ti-Fe-B的组织形貌、显微硬度及其物相分布等的影响。通过采用光学显微镜、扫描电子显微镜、维氏硬度计和X射线衍射仪等观察了在不同温度下退火后超细晶Ti-Fe-B的组织形貌、维氏硬度及物相分布的变化。研究结果表明：

（1）不同退火温度下合金组织均由暗灰色的α相和亮白色β相组成。

（2）不同退火温度下合金的显微硬度变化较明显，呈现出先增加后减小的趋势，当退火温度为400℃时，显微硬度出现最大值。

（3）X射线衍射谱中只有α相和β相的衍射峰，并无其他衍射峰存在，说明低温短时退火并不会导致新相的生成。α相对应的衍射峰的强度不断增强，其中α（101）衍射峰的强度增加尤为明显。β相对应的衍射峰的强度呈现先增加后降低的趋势，当退火温度为300℃时，β（110）衍射峰的强度最强。

关键词：超细晶钛合金Ti-Fe-B 低温短时退火 组织形貌 维氏硬度

The effect of heat treatment on Microstructure and mechanical properties of ultrafine Ti-Fe-B alloy

Abstract

Titanium alloy has the characteristics of small density, high specific strength, small elastic modulus, non-magnetic, corrosion resistance, high temperature creep performance, etc. It is widely used in biomedical, petrochemical, aerospace and other fields, and its performance advantages are also increasing Significantly. However, titanium alloys also have some defects, such as poor plasticity at low temperatures, complicated processing and production technology, long cycle time, low yield rate, and a large amount of residual materials in the production process, which further increases the cost of their use. Therefore, the cost issue has become another important factor restricting the wide application of titanium alloys. Fine grain strengthening is one of the important ways to improve the strength and performance of metal materials. Equal Channel Angular Pressing (ECAP) technology, as a new plastic processing method, can be used without changing the size of the material. The sample undergoes severe plastic deformation (Severe Plastic Deformation, abbreviation: SPD), which accumulates a large amount of strain and reduces the grain size, thereby effectively refining the grain, improving the structure and composition distribution, and greatly improving the strength and comprehensive mechanical properties of the material It can also avoid metallurgical defects and cost problems caused by the addition of alloy elements. After processing, general materials will produce crystal defects such as dislocation tangling and stress concentration. Heat treatment of metal materials can effectively eliminate crystal defects generated during production and processing, thereby improving the performance of the material. For traditional coarse-grained materials, annealing treatment will reduce the strength of the material. However, the ultra-fine grain titanium alloy is annealed at low temperature for a short time, which not only does not reduce the strength of the material, but also effectively suppresses the growth of the material grains, resulting in the abnormal hardening of the ultra-fine grain titanium alloy, which makes its performance more excellent.

This subject mainly studies the effect of short-time annealing at low temperature on the microstructure, microhardness and phase distribution of the ultrafine-grained titanium alloy Ti-Fe-B prepared by ECAP. The changes of microstructure, Vickers hardness and phase distribution of ultrafine grain Ti-Fe-B after annealing at different temperatures were observed by using optical microscope, scanning electron microscope, Vickers hardness tester and X-ray diffractometer. . Research indicates:

(1) The alloy structure is composed of dark gray α phase and bright white β phase at different annealing temperatures.

(2) The microhardness of the alloy changes significantly at different annealing temperatures, showing a trend of increasing first and then decreasing. When the annealing temperature is 400 ℃, the microhardness shows the maximum value.

(3) In the X-ray diffraction spectrum, there are only the diffraction peaks of α-phase and β-phase, and there are no other diffraction peaks, indicating that short-term annealing at low temperature will not lead to the formation of new phases. The intensity of the diffraction peak corresponding to α continues to increase, and the increase in the intensity of the α(101) diffraction peak is particularly obvious. The intensity of the diffraction peak corresponding to β shows a tendency to increase first and then decrease. When the annealing temperature is 300 °C, the intensity of the β(110) diffraction peak is the strongest.

Keywords: Ultrafine grained titanium alloy Ti-Fe-B; Low temperature short-time annealing; Microstructure morphology; Vickers hardness.

目 录

摘 要 I

Abstract III

第一章 绪论 1

1.1 引言 1

1.2等通道转角挤压技术 1

1.2.1等通道转角挤压技术的原理 1

1.2.2等通道转角挤压技术的研究现状 2

1.2.3 ECAP对组织的影响 3

1.2.4 ECAP对力学性能的影响 4

1.3 ECAP变形参数 4

1.3.1挤压次数 4

1.3.2模具通道转角 4

1.3.3挤压温度 5

1.3.3挤压速率 5

1.4 钛合金的热处理工艺 5

1.5低温退火对超细晶钛合金组织的影响 6

1.6课题研究目的及研究内容 6

1.6.1课题的研究目的 6

1.6.2课题的研究内容 7

第二章 实验材料与实验方法 8

2.1 实验材料 8

2.1.1 合金成分 8

2.1.2 超细晶合金的制备 8

2.1.3合金的热处理 9

2.2实验方法 10

2.2.1 扫描电子显微镜观察 10

2.2.2 维氏硬度测试 10

2.2.3 X射线衍射分析 11

第三章 热处理对Ti-Fe-B合金组织和性能的影响 13

3.1 合金微观组织形貌观察 13

3.2 合金的显微维氏硬度分析 14

3.3 合金X射线衍射分析 14

第四章 结论 17

参考文献 18

致谢 21

第一章 绪论

1.1 引言

钛是一种性能优异的金属，它具有优秀的力学性能以及耐腐蚀性能。钛元素在地壳中的含量约0.6%，在结构金属的丰度量上排列第四，仅次于铝、铁和镁。钛合金的密度较低，大致相当于铁合金或镍合金密度的一半，因而钛合金的比强度较高^[1,2]。然而，其成本相对于传统金属较高，在很大程度上限制了其更广泛的使用。因此，钛及其合金的使用率仍然是有限的。钛合金也存在一些缺陷，钛合金在低温下的塑性较差，无法达到某些领域所需求的高强度、高塑性变形能力的指标，这是限制其广泛应用的一个重要因素。另外，钛合金加工生产工艺复杂，生产周期较长，成材率低，生产过程中伴随大量残料的生成，进一步增加了其使用成本。因此，成本成为制约钛合金广泛应用的根本性问题。

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