EFFECT OF SULPHURIZING-OXIDIZING ENVIRONMENT ON CREEP CRACK GROWTH OF Ni-BASE SUPERALLOY GH30

An investigation was made on the creep crack growth behaviour under static load at 1023 Kfor Ni-base superalloy GH30 exposed to air and air+10% SO_2.The results showed that inthe region of low stress intensity factor,the creep crack growth rate is higher in air+10%SO_2 than in air only,while in the high region,it is reverse.The fractograph of specimens hasbeen analyzed,and the mechanism of creep crack growth together with the influences of sul-phur and oxygen has been discussed as well.     

硫-氧化环境对GH30镍基高温合金蠕变裂纹扩展行为的影响SCIEI

研究了GH30镍基高温合金在静载荷下在1023K不同气氛中的蠕变裂纹扩展行为。结果表明:低应力强度因子区域,在10％SO_2+空气中的da/dt比空气中的高;高应力强度因子区域的da/dt,则与上述相反。对断口进行了分析,并讨论了蠕变裂纹扩展机制以及硫、氧的影响。     

FATIGUE CRACK PROPAGATION OF Ni-BASE SUPERALLOYS

Time-dependent Fatigue Crack Propagation (FCP) behaviors of five Ni-base superalloys were investigated at various temperatures under fatigue with various holding times and sustained loading conditions. The new concept of damage zone is defined and employed to evaluate the alloys‘ resistance to hold-time FCP. A special testing procedure is designed to get the maximum damage zone of the alloys. Udimet 720 and Waspaloy show shorter damage zones than alloys 706 and 718. The fractographieal analyses show that the fracture surfaces of the specimens under hold-time fatigue conditions are mixtures with intergranular and transgranular modes. As the extension of holding time per cycle, the portion of intergranular fracture increases, The effects of loading stress intensity, temperature, holding time, alloy chemisty, and alloy microstructure on damage zone and the crack growth behaviors are studied. Hold-time usually increases the alloy‘s FCP rate, but there are few exemptions. For instance, the steady, state hold-time FCP rate of Waspaloy at 760℃ is lower than that without hold-time. The beneficial effect of hold-time was attributed to the creep caused stress relaxation during the hold-time.     

EFFECT OF NON-PROPORTIONAL OVERLOADING ON FATIGUE CRACK GROWTH

The effect of proportional and non-proportional overloading on mode l fatigue crack growthhave been studied,and the influences of crack tip plastic zone,crack tip blunting as well ascrack closure were discussed.Proportional(model I)overloading may cause more seriouscrack growth retardation than non-proportional(mixed mode)overloading.Therefore,forestimating the fatigue life of engineering structures to simplify a real overload which may of-ten be non-proportional as a proportional one is not always safe.     

细晶处理对镍基合金疲劳蠕变交互作用行为的影响

本文研究了两种晶粒度的GH 698合金在700℃疲劳蠕变交互作用下的断裂寿命和形变行为.结果表明:在疲劳蠕变应力交互作用下的断裂寿命可以分成F,FC和C三个区.在FC及C区,交变应力的存在明显地阻碍蠕变形变过程,提高了断裂寿命.细晶处理后使这种阻碍作用加强,断裂寿命提高幅度变大.在大应力的疲劳区进行细晶处理,反而使合金寿命降低.     

ASPECTS OF FATIGUE CRACK GROWTH IN INTERMET ALLICALLOYS

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高温合金GH169时间相关疲劳中氧化作用及其微观机制SCIEI

本文研究了高温合金GH169 650℃下时间相关疲劳中氧化作用及其微观机制。试验表明,在相同应力和保持时间下,氩气中的循环寿命均低于大气中的循环寿命,损伤机制主要是高温氧化-疲劳交互作用。在高温大气中的断口表面覆盖有致密而均匀的氧化膜;而在高温氩气中的断口表面则为不连续氧化物质点。     

TIME-DEPENDENT FATIGUE AND ITS MICROMECHANISM OF SUPERALLOY GH169 UNDER OXIDATION

The time-dependent fatigue and its micromechanism of superalloy GH169 at 650℃ have beenstudied.Under the same stress and duration,its cyclic life in Ar is shorter than that in air.Thedamage mechanism is mainly of the interaction between high temperature oxidation and fa-tigue.The fracture surface of GH169 specimen oxidized at 650℃ in air is revealed to be cov-ered with a dense and even oxide film,but in Ar,with uncontinuous oxide particles.As thetime prolonged,the Cr_2O_3 content in the surface oxides increases in air and decreases in Ar.     

GH901合金的蠕变裂纹扩展

我们对GH135合金的高温长期实验结果表明,存在一个“开裂界限”K_(It)(或称K_(Ihcc))。当应力强度因子K_I相似文献   

EFFECTS OF TRACE Zr ON FATIGUE CRACK GROWTH RATE OF HIGH DAMPING Zn-Al ALLOY

ＥＦＦＥＣＴＳＯＦＴＲＡＣＥＺｒＯＮＦＡＴＩＧＵＥＣＲＡＣＫＧＲＯＷＴＨＲＡＴＥＯＦＨＩＧＨＤＡＭＰＩＮＧＺｎ－ＡｌＡＬＬＯＹ￥ＺｈｏｕＳｈａｎｃｈｕ；ＬｕｏＢｉｎｇｈｕｉ（ＤｅｐａｒｔｍｅｎｔｏｆＭａｔｅｒｉａｌｓＳｃｉｅｎｃｅａｎｄＥｎｇｉｎｅｅ...     

少量Mg和Zr对一种Ni-Cr-Ti型变形合金蠕变裂纹长大行为的影响

采用电位法测定单边切口试样700℃下的蠕变裂纹生长,并测定裂纹起始寿命和断裂寿命(t_(rc)和t_r)。用能量率积分(C~*)描述稳态蠕变条件下裂纹顶端附近的场。给出裂纹长大速率与C~*的函数关系,预报的裂纹起始时间与实测值相符。发现合金中加入少量Mg和Zr可以大大延长蠕变裂纹起始寿命和蠕变断裂寿命。     

高强度钢压剪疲劳裂纹扩展的实验研究

滚珠轴承接触点附近的高压剪应力是引起轴承疲劳破坏的原因。为获得高强度钢在压剪疲劳加载下的断裂性态,通过轴向裂纹薄壁圆筒的压剪疲劳加载试验,研究了这类材料的疲劳破坏规律。结果表明,复合疲劳加载时门槛值对压应力分量并不敏感,但对扩散速率和临界扩展角却有明显影响。裂纹扩展速率随压应力增加而提高,裂纹较快达到失稳;裂纹扩散角则随压应力增加而减小,疲劳裂纹将向有利于Ⅰ型断裂的方向扩展。这表明轴承滚道内,任何平行于压应力的缺陷、微裂纹都将是十分危险的。     

HIGHTEMPERATURE LOWCYCLE FATIGUE BEHAVIOR OF NICKELBASED SUPERALLOY GH4049

１．ＩｎｔｒｏｄｕｃｔｉｏｎＧＨ４０４９ｉｓａｗｒｏｕｇｈｔｎｉｃｋｅｌｂａｓｅｄｓｕｐｅｒａｌｏｙｉｎｗｈｉｃｈγ′ｈａｓｂｅｅｎｉｄｅｎｔｉｆｉｅｄａｓｔｈｅｐｒｉｍａｒｙｓｔｒｅｎｇｔｈｅｎｉｎｇｐｈａｓｅ．Ｓｉｎｃｅｔｈｉｓａｌｏｙｅｘｈ...     

残余压应力场中疲劳短裂纹扩展模型及实验

结合实验讨论了残余应力对裂纹扩展作用的模型及其存在的问题。指出用公式△Ｋｅｆｆ＝（Ｋｍａｘ＋λＫｒ）－Ｋｏｐ中较准确地计算出残余压应力场中裂纹的扩展速率。残余压应力既使裂纹闭合力提高，又使最大应力强度因子降低，两者均使裂纹扩展驱动力△Ｋｅｆｆ减少，因而降低了裂纹的扩展速率。     

应力比和频率对低合金钢腐蚀疲劳裂纹扩展机理的影响

在理论分析裂尖局部应变、应变速率及溶解速度的基础上、实验测定了低合金钢ZG20SiMn,SM50B—Zc的腐蚀疲劳裂纹扩展速率,并随着裂纹的扩展测定了裂纹内和裂纹尖端的pH值和金属电极电位、指出降低频率和增加应力比所导致的腐蚀疲劳裂纹扩展速率的增加部分主要来自于氢脆的加速作用     

EFFECT OF Mg AND Zr ADDITION ON CREEP CRACK GROWTH BEHAVIOUR OF A Ni-BASE SUPERALLOY

The creep crack growth(CCG)and the time to carck initiation and rupture of specimen(t_(rc)and t_r)were measured by means of electrical potential method on single edge notchedspecimens at 700℃.The field near the crack tip under steady-state creep was represented byenergy rate integral(C~*),and the CCG rate as a function of C~* has been obtained.Theagreement between the predicted and observed t_(rc)values is quite good.It was found that theaddition of small amount of Mg and Zr in the alloys causes t_(rc)and t_r of the specimens to in-crease significantly.     

EFFECT OF GRAIN REFINING ON FATIGUE-CREEP INTERACTION BEHAVIOURIN A Ni-BASE SUPERALLOY

The fatigue-creep interaction behaviour of superalloy GH698 with different grain sizes hasbeen studied at 700℃.The results show that three zones,F,C and FC,can be distinguished atthe fatigue-creep interaction curves.In zones FC and C,the presence of alternative stressesinhibits the creep deformation process therefore delays the fracture of the alloy.This effectwill be enhanced by grain refining.However,in zone F,grain refining exhibits an inverse effect under large alternative stresses.     

垂直晶界和倾斜晶界Cu双晶的疲劳开裂行为及其机制

用扫描电镜（ＳＥＭ）研究了一种垂直晶界和两种倾斜晶界Ｃｕ双晶的疲劳开裂行为及其机制。这三种双晶组元晶体的取向均为「１３４」。结果表明,沿晶界的疲劳开裂是Ｃｕ双晶疲劳破坏的主要形式,但垂直晶界和倾斜晶界双晶疲劳裂纹萌生的机制有所不同。垂直晶界双晶沿晶疲劳裂纹主要由驻留滑移带撞击晶界面产生,而倾斜晶界双晶疲劳裂纹的萌生是由晶界两侧晶粒的滑移台阶而引起的应力集中所致。造成这种差别的原因同两种双晶的活动滑     

疲劳裂纹扩展的非比例过载效应SCIEI

本工作研究了比例(Ⅰ型)过载及非比例(复合型)过载对常幅Ⅰ型疲劳裂纹扩展的影响。结果表明:Ⅰ型过载所引起的裂纹滞后扩展效应远较复合型为强。因此,在估算疲劳寿命时将零、构件实际承受的过载(大都为非比例过载)简单地当作比例过载处理,可能会过高地估计寿命,带来不安全因素。文章从Ⅰ型及复合型过载所引起的裂纹钝化、裂端塑性区的形状、尺寸及裂纹闭合等方面讨论了它们对裂纹扩展滞后效应的影响。     

HIGH-TEMPERATURE LOW CYCLE FATIGUE BEHAVIOR OFNICKEL BASE SUPERALLOY GH536

1. IntroductionGH536 is a nickel base superalloy with good oxidation and corrosion resistances. Atelevated temperature up to 900wr, it has middle stress-rupture and creep strengths. Thisalloy has been widely used for flame and other high temperature parts in aircraft engines.Since these components are operated in high temperature and subjected to varying loads,the damage from high temperature low cycle fatigue is one of the factors affecting theservice life of these componellts. Many research…