CN114813329A - A residual life prediction method for nickel-based single crystal superalloys under random creep loading - Google Patents

Abstract

The invention relates to a method for predicting the remaining life of a nickel-based single crystal superalloy under random creep loads, including: (1) carrying out full-life creep tests and interrupted creep tests of standard parts under different loads, and obtaining the matrix under different loads Phase channel width-time curve; (2) Dimensionless creep time under different loads is obtained to obtain the matrix phase channel width-normalized time curve; (3) The matrix phase channel width-normalized time function equation is obtained ; (4) For a batch of standard parts subjected to random creep loads, select some of the standard parts to obtain the average value of the matrix phase channel width of the standard parts; (5) The average value of the matrix phase channel width obtained in (4) is taken Entering the matrix phase channel width-normalized time function equation established in (3), combined with the time that the current standard parts have been subjected to random creep load, the remaining life of the batch of standard parts under the same random creep load can be obtained.

Description

A residual life prediction method for nickel-based single crystal superalloys under random creep loading

technical field

The invention belongs to the technical field of high-temperature mechanical property prediction of materials and aero-engines, and particularly relates to a method for predicting remaining life under random creep load of nickel-based single crystal superalloy.

Background technique

Nickel-based single crystal superalloys are widely used in the manufacture of aero-engine and gas turbine turbine blades. Nickel-based single crystal turbine blades are subjected to centrifugal loads in a high temperature environment, and creep will inevitably occur. The research shows that creep is one of the important failure modes of nickel-based single crystal turbine blade airfoil. Therefore, accurate prediction of the creep life of nickel-based single crystal superalloys is of great significance for the life design and evaluation of nickel-based single crystal turbine blades.

(K为常数，t_ri为在i条件下运行时的断裂时间、只取决于温度和应力的水平，t_i为在i条件下的运行时间)时，认为材料达到蠕变寿命。但是，常数K不一定恒定为1(也可能是2到4)，这导致基于该方法的蠕变寿命预测结果偏差较大(李益民，束国刚，梁昌乾.电站高温部件蠕变寿命预测方法现状.热力发电，1994(2):38-44)。In terms of creep life prediction, domestic and foreign scholars have carried out a lot of work. The mathematical relationship between rupture time and stress is usually established based on the creep test results of standard parts, and the creep life under constant isothermal load is predicted accordingly. Combined with the creep rupture time under different loads, the life under random creep loads can be predicted based on the damage accumulation theory.

(K is a constant, t _ri is the fracture time when operating under i conditions, which only depends on the temperature and stress level, and t _i is the operating time under i conditions), the material is considered to have reached the creep life. However, the constant K is not necessarily constant at 1 (it may also be 2 to 4), which leads to a large deviation of the creep life prediction results based on this method (Li Yimin, Shu Guogang, Liang Changqian. Current Situation of Creep Life Prediction Methods for High-temperature Components in Power Plants) . Thermal Power Generation, 1994(2):38-44).

The present invention provides a new method for predicting the residual life of nickel-based single crystal superalloy under random creep load. The residual life under variable load is predicted. The matrix phase channel width-normalized time function equation has nothing to do with the load, and is suitable for predicting the residual life of standard parts under different creep loads (including random creep loads).

It can be seen from the above that the creep life prediction methods in the prior art are usually aimed at predicting the remaining life under constant creep load, and some methods that can predict the remaining life under random creep load are usually based on the damage accumulation theory, and the accuracy of the life prediction results is relatively high. Low.

SUMMARY OF THE INVENTION

In order to overcome the deficiencies of the prior art, the present invention provides a method for predicting the residual life of a nickel-based single crystal superalloy under random creep loads, which can effectively realize the residual life of standard parts under different creep loads (including random creep loads). The prediction is expected to serve the design and evaluation of the creep life of advanced aero-engine turbine blades.

The technical solution of the present invention: a residual life prediction method under random creep load of nickel-based single crystal superalloy. The remaining life under variable load (including random creep load) is predicted. The specific implementation steps are as follows:

The first step is to carry out the full-life creep test and the interrupted creep test of the standard parts under different loads. Based on the scanning electron microscope, the width of the matrix phase channel at different stages of creep is measured, and the width-time curve of the matrix phase channel under different loads is obtained. ;

In the second step, the creep time under different loads is dimensionless, and the matrix phase channel width-normalized time curve is obtained;

The third step is to fit the matrix phase channel width-normalized time curve to obtain the matrix phase channel width-normalized time function equation;

The fourth step, for a batch of standard parts subjected to random creep load, select some of the standard parts, measure the channel width of the matrix phase based on the scanning electron microscope, and obtain the average value of the channel width of the matrix phase of the standard parts;

The fifth step is to bring the average value of the matrix phase channel width obtained in the fourth step into the matrix phase channel width-normalized time function equation established in the third step to obtain the normalized corresponding to the standard part currently subjected to random creep load. The normalization time, combined with the time that the current standard parts have been subjected to random creep load, can obtain the remaining life of the batch of standard parts under the same random creep load.

Further, the matrix phase channel width-normalized time function equation is expressed as follows:

为归一化时间，a、b、c为材料常数。where w is the channel width of the matrix phase,

is the normalized time, and a, b, and c are material constants.

Compared with the prior art, the advantages of the present invention are: the present invention predicts the residual life of nickel-based single crystal superalloy standard parts under random creep load based on the matrix phase channel width-normalized time function equation, and is a nickel-based single crystal superalloy standard part. The residual life prediction of single crystal superalloys under random creep loading provides a new idea. The evolution of the matrix channel width with the normalized time is independent of the load, so the matrix channel width-normalized time function equation can theoretically describe the evolution law of the matrix channel width with the normalized time under any creep load. The residual life prediction of standard parts under different creep loads (including random creep loads), and the accuracy of the life prediction results is high.

Description of drawings

Fig. 1 is a kind of implementation process flow of remaining life prediction method under random creep load of nickel-based single crystal superalloy according to the present invention;

Fig. 2 is a schematic diagram of the channel width of the matrix phase of the nickel-based single crystal superalloy;

Fig. 3 shows the channel width-time curves of the matrix phase under different loads;

Figure 4 is the matrix phase channel width-normalized time curve under different loads;

Fig. 5 is the fitting result of matrix phase channel width-normalized time curve;

Figure 6 is a schematic diagram of random creep load;

Fig. 7 is a schematic diagram of a failure risk region and an adjacent failure region in a matrix phase channel width-normalized time diagram;

Figure 8 shows the current normalized time prediction results and their upper and lower limits when the average matrix phase channel width is 0.16 μm;

Figure 9 shows the residual life prediction results and their upper and lower limits when the average matrix phase channel width is 0.16 μm;

Figure 10 shows the current normalized time prediction results and their upper and lower limits when the average matrix phase channel width is 0.12 μm;

Figure 11 shows the predicted results of the remaining life and its upper and lower limits when the average matrix phase channel width is 0.12 μm.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

In the following, the technical scheme of the method for predicting the residual life under random creep load of nickel-based single crystal superalloy proposed by the present invention will be further described by way of example with reference to the accompanying drawings. The pre-studied material in this example is a nickel-based single crystal superalloy CMSX4.

As shown in Figure 1, the specific implementation process of the present invention is as follows:

The first step is to carry out the full-life creep test and interrupted creep test of standard parts under different loads. Matrix channel width-time curve (shown in Figure 3).

In the second step, the creep time under different loads is dimensionless, and the matrix phase channel width-normalized time curve is obtained (as shown in Figure 4). It can be seen from Fig. 4 that the matrix phase channel width-normalized time curves under different loads conform to the same law, which means that the evolution of the matrix phase channel width with normalized time is independent of the load.

The third step is to fit the matrix phase channel width-normalized time curve to obtain the matrix phase channel width-normalized time function equation. The matrix phase channel width-normalized time function equation is as follows:

为归一化时间，a、b、c为材料常数。当a＝0.1295、b＝0.5694、c＝-0.0607时，基体相通道宽度-归一化时间曲线的拟合结果如图5所示。图中阴影部分涵盖了不同载荷下的基体相通道宽度测量结果，其上下边界代表采用该拟合方程进行预测时的偏差上限和下限。如前所述，基体相通道宽度随归一化时间的演化与载荷无关，因此基体相通道宽度-归一化时间函数方程理论上可以描述任意蠕变载荷下基体相通道宽度随归一化时间的演化规律。where w is the channel width of the matrix phase,

is the normalized time, and a, b, and c are material constants. When a=0.1295, b=0.5694, and c=-0.0607, the fitting results of the matrix phase channel width-normalized time curve are shown in Fig. 5 . The shaded part in the figure covers the measurement results of the channel width of the matrix phase under different loads, and the upper and lower bounds represent the upper and lower deviation limits of the prediction using the fitting equation. As mentioned above, the evolution of the matrix channel width with normalized time is independent of the load, so the matrix channel width-normalized time function equation can theoretically describe the matrix channel width with normalized time under any creep load. evolution law.

The fourth step, for a batch of standard parts subjected to random creep load (as shown in Figure 6), select some of the standard parts, and measure the channel width of the matrix phase based on the scanning electron microscope to obtain the width of the matrix phase channel of the standard parts. average value.

The fifth step is to bring the average value of the matrix phase channel width obtained in the fourth step into the matrix phase channel width-normalized time function equation established in the third step to obtain the normalized corresponding to the standard part currently subjected to random creep load. The normalization time, combined with the time that the current standard parts have been subjected to random creep load, can obtain the remaining life of the batch of standard parts under the same random creep load.

It should be pointed out that during the service process of the real structure, when there is a risk of failure or near failure, the real structure will usually not be used. Therefore, the method proposed in the present invention does not perform remaining life prediction for standard parts with failure risk and standard parts that are close to failure. As shown in Figure 7, when the channel width of the matrix phase reaches about 0.17, the lower boundary of the shaded part has reached the maximum normalization time, which means that the standard part has a risk of failure at this time; in addition, when the normalization time reaches 0.9, It is considered that the standard part is close to failure at this time.

When the average matrix phase channel width is 0.16 μm, based on the matrix phase channel width-normalized time function equation, the normalized time at this time can be calculated to be 0.79. The calculated deviation at this time can be combined with the upper and lower parts of the shaded part in Fig. 5. The lower boundary is determined (as shown in Figure 8), the lower limit of the normalization time after considering the calculation deviation is 0.60, and the upper limit of the normalization time after considering the calculation deviation is 0.90. Assuming that the batch of standard parts has been subjected to random creep load for 200 hours, its remaining life is:

200(hours)/0.79×(1-0.79)=53.16(hours)

The upper limit of the remaining life after accounting for the calculated deviation is:

200(hours)/0.60×(1-0.60)=133.33(hours)

The lower limit of the remaining life after considering the calculated deviation is:

200(hours)/0.90×(1-0.90)=22.22(hours)

Combining with the upper and lower limits of the remaining life after considering the calculated deviation, it can be seen that the predicted result of the remaining life is within the 3-fold dispersion band (as shown in Figure 9).

When the average matrix phase channel width is 0.12 μm, based on the matrix phase channel width-normalized time function equation, the normalized time at this time can be calculated as 0.32. The calculation deviation at this time can be combined with the upper and lower parts of the shaded part in Fig. 5. The lower boundary is determined (as shown in Figure 10), the lower limit of the normalized time after considering the calculated deviation is 0.21, and the lower limit of the normalized time after considering the calculated deviation is 0.44. Assuming that the batch of standard parts has been subjected to random creep load for 200 hours, its remaining life is:

200(hours)/0.32×(1-0.32)=425.00(hours)

The upper limit of the remaining life after accounting for the calculated deviation is:

200 (hours)/0.21×(1-0.21)=752.3 (hours)

The lower limit of the remaining life after considering the calculated deviation is:

200(hours)/0.44×(1-0.44)=254.44(hours)

Combining with the upper and lower limits of the remaining life after considering the calculated deviation, it can be seen that the prediction result of the remaining life is within the 2-fold dispersion band (as shown in Figure 11).

Generally, when the life prediction result under random creep load is within the 3 times dispersion band, the life prediction method is considered to have higher accuracy; the present invention can not only predict the remaining life of nickel-based single crystal superalloy under different constant creep loads , and can predict the residual life of nickel-based single crystal superalloys under random creep loading.

The above embodiments are provided for the purpose of describing the present invention only, and are not intended to limit the scope of the present invention. The scope of the invention is defined by the appended claims. Various equivalent replacements and modifications made without departing from the spirit and principle of the present invention should be included within the scope of the present invention.

Claims (2)

1. The method for predicting the residual life of the nickel-based single crystal superalloy under the random creep load is characterized by comprising the following steps of:

step (1): carrying out a full-life creep test and an interruption creep test of the standard component under different loads, measuring the width of the matrix phase channel at different stages of creep on the basis of a scanning electron microscope, and acquiring matrix phase channel width-time curves under different loads;

step (2): carrying out dimensionless transformation on creep time under different loads to obtain a matrix phase channel width-normalization time curve;

and (3): fitting a matrix phase channel width-normalization time curve to obtain a matrix phase channel width-normalization time function equation;

and (4): selecting a part of standard parts subjected to random creep load, measuring the matrix phase channel width of the standard parts based on a scanning electron microscope, and obtaining the average value of the matrix phase channel width of the standard parts;

and (5): and (4) substituting the average value of the matrix phase channel width obtained in the step (4) into the matrix phase channel width-normalization time function equation established in the step (3), obtaining the normalization time corresponding to the standard component currently subjected to the random creep load, and obtaining the residual life of the batch of standard components under the same random creep load by combining the time that the current standard component has been subjected to the random creep load.

2. The method for predicting the residual life under the random creep load of the nickel-based single crystal superalloy as claimed in claim 1, wherein: the matrix phase channel width-normalized time function equation in the step (3) is expressed as follows:

wherein w is the width of the matrix phase channel,

for normalized time, a, b, c are material constants.

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