本文選題：硬質(zhì)合金 + 小能多沖��； 參考：《湖南大學》2016年碩士論文

【摘要】：硬質(zhì)合金以其優(yōu)良的綜合性能被廣泛用于工業(yè)上,被譽為工業(yè)上的牙齒。硬質(zhì)合金工具常處于小能量多次沖擊碰撞的工況,所以研究硬質(zhì)合金工具在小能量下服役的性能意義重大。本文以株洲硬質(zhì)合金集團有限公司提供的六種WC-Co硬質(zhì)合金為研究對象,對硬質(zhì)合金進行兩種實驗方案的小能多沖實驗以及硬質(zhì)合金材料研究較少的靜疲勞實驗。另外分析了斷口的宏觀與微觀斷裂行為并探討了粉末冶金缺陷對硬質(zhì)合金性能的影響。主要研究結(jié)論如下：(1)實驗合金力學性能測試結(jié)果表明：相同WC晶粒尺寸的硬質(zhì)合金,隨著Co含量的增多,其沖擊韌性、抗彎強度與斷裂韌性得到提高,硬度下降。相同Co含量的硬質(zhì)合金,隨著WC晶粒尺寸的增大,其硬度、沖擊韌性、抗彎強度反而減小,斷裂韌性得到提高。(2)兩種小能多沖實驗方案結(jié)果表明：實驗合金在相同能量下沖擊,Co含量越高,硬質(zhì)合金小能多沖壽命越長,WC晶粒尺寸越大,小能多沖壽命越短：實驗合金在相同的λ值(沖擊能量與一次沖斷能量的比值)對應(yīng)能量下沖擊,Co含量越高,小能多沖壽命越短,WC晶粒尺寸越大,小能多沖壽命短。Co含量最高的218#合金具有較高的疲勞敏感性,抗疲勞裂紋擴展能力較弱：Co含量最低的211#合金具有較低的疲勞敏感性,抗疲勞裂紋擴展能力較強。在工程技術(shù)上,這也表明高鈷合金在服役條件下需要選擇更高的安全系數(shù)。(3)通過對三種不同鈷含量(11wt%,15wt%,18wt%)的硬質(zhì)合金進行缺口樣和光滑樣的靜疲勞性能研究對比,得出：合金在相同應(yīng)力下靜壓,Co含量越高,靜疲勞壽命越長,在相同θ值(施壓在樣品上的靜態(tài)應(yīng)力與該樣品的抗彎強度之比)下靜壓,Co含量越高,靜疲勞壽命越短,Co含量較低的211#合金有較低的疲勞敏感性,抗疲勞裂紋擴展能力較強。三種帶缺口試樣靜疲勞壽命明顯低于光滑試樣,且在θ值為0.8時,鈷含量為18wt%,15wt%,11wt%的三種合金光滑樣與缺口樣的靜疲勞壽命比值分別約為1：2：7與1：1：2,這說明了缺口預制試樣掩蓋了硬質(zhì)合金的缺陷。(4)硬質(zhì)合金在小能量下服役(小能多沖與靜疲勞試驗)導致其斷裂是由于內(nèi)部孔洞(或粗大WC之類的缺陷)與實驗過程中產(chǎn)生的缺陷在累積受力情況下慢慢長大,孔洞相互連接形成微裂紋,微裂紋慢慢長大達到臨界裂紋長度時導致材料斷裂。
[Abstract]:Cemented carbides are widely used in industry because of their excellent comprehensive properties. Cemented carbide tools are often in the condition of low energy impact and collision, so it is of great significance to study the performance of cemented carbide tools under low energy. In this paper, six kinds of WC-Co cemented carbides provided by Zhuzhou cemented Carbide Group Co., Ltd are taken as the research object. The small energy multi-impact experiments of two experimental schemes and the static fatigue tests of cemented carbide materials are carried out. In addition, the macroscopic and microscopic fracture behavior of fracture surface was analyzed and the influence of powder metallurgy defects on the properties of cemented carbide was discussed. The main conclusions are as follows: (1) the mechanical properties of the alloy show that the impact toughness, flexural strength and fracture toughness of the cemented carbide with the same WC grain size increase with the increase of Co content, and the hardness decreases. The hardness, impact toughness and bending strength of cemented carbides with the same Co content decrease with the increase of WC grain size. The experimental results of two kinds of small energy multiple impact test schemes show that the higher the impact Co content at the same energy, the longer the small energy multi-impact life of cemented carbides and the larger the WC grain size. The shorter the small energy multi-impact life is, the higher the impact Co content is at the same 位 value (the ratio of impact energy to primary thrust energy), and the smaller the small energy multi-impact life is, the larger the WC grain size is. The 218# alloy with the highest content of low energy multi-impact life has higher fatigue sensitivity, and the 211# alloy with the weakest crack growth resistance has lower fatigue sensitivity and stronger anti-fatigue crack propagation ability than the 211# alloy with the lowest fraction of small energy and multi-impact life, and the fatigue crack growth resistance of 218# alloy is higher than that of 211# alloy with the lowest fraction of small energy multi-impact life. In engineering technology, this also indicates that the high cobalt alloy needs to select a higher safety factor under service conditions.) by comparing the static fatigue properties of three kinds of cemented carbides with different cobalt contents of 11 wtt and 15 wtt and 18 wtts, the static fatigue properties of notched and smooth samples are studied and compared. It is concluded that the higher the content of Co under the same stress, the longer the static fatigue life of the alloy, and the higher the content of Co in the static pressure at the same 胃 value (the ratio of the static stress applied on the sample to the bending strength of the sample). The shorter the static fatigue life, the lower the fatigue sensitivity of 211# alloy, and the stronger the fatigue crack growth resistance. The static fatigue life of three notched specimens is obviously lower than that of smooth specimens, and when 胃 value is 0.8, The ratios of static fatigue life of three kinds of alloys with cobalt content of 18 wt% and 11wt% are about 1:2:7 and 1: 1: 2, respectively, indicating that the notched prefabricated specimens cover the defects of cemented carbides. Static fatigue test) the fracture is caused by internal holes (or defects such as large WC) and the defects produced in the course of experiments, which grow slowly under cumulative stress. The pores are connected to each other to form microcracks, and when the microcracks grow up to the critical crack length, they lead to the fracture of the material.
【學位授予單位】：湖南大學
【學位級別】：碩士
【學位授予年份】：2016
【分類號】：TG135.5

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