阅读说明：本技术 一种具有深层高压应力的强化微晶玻璃及其制备方法 (Reinforced microcrystalline glass with deep high-pressure stress and preparation method thereof ) 是由 王键 林美灵 张熊熊 黄小杰 洪立昕 于 2020-06-09 设计创作，主要内容包括：本发明涉及了一种具有深层高压应力的强化微晶玻璃及其制备方法,包括两个对应的压缩应力层；所述压缩应力层由上下表面向内延伸,依次包括表面压缩应力区和深层压缩应力区；所述表面压缩应力区和深层压缩应力区的总厚度为50～100um；所述表面压缩应力区的厚度为20um,所述表面压缩应力区的应力CS≥800MPa；所述深层压缩应力区中,内应力分布斜率的绝对值＜2,CS-30≥115MPa,CS-50≥80MPa,其CT值介于50-90MPa,维氏硬度大于6.50GPa,4PB测试值大于700N/mm<Sup>2</Sup>,单杆静压强度损失率小于10％,(500kgf/15s下的预制缺陷),断裂阀值大于5kgf,极大改善了强化微晶玻璃的相关性能。其制备包括两次离子交换步骤。(The invention relates to a strengthened microcrystalline glass with deep high-pressure stress and a preparation method thereof, wherein the strengthened microcrystalline glass comprises two corresponding compressive stress layers; the compressive stress layer extends inwards from the upper surface and the lower surface and sequentially comprises a surface compressive stress region and a deep layer compressive stress region; the total thickness of the surface compressive stress region and the deep compressive stress region is 50-100 um; the thickness of the surface compressive stress region is 20um, and the stress CS of the surface compressive stress region is more than or equal to 800 MPa; the deep layerIn the compressive stress region, the absolute value of the internal stress distribution slope is less than 2, CS-30 is more than or equal to 115MPa, CS-50 is more than or equal to 80MPa, the CT value is 50-90MPa, the Vickers hardness is more than 6.50GPa, and the 4PB test value is more than 700N/mm 2 The loss rate of the single-rod static pressure strength is less than 10 percent, (prefabricated defects under 500kgf/15 s), the fracture threshold value is more than 5kgf, and the related performance of the reinforced glass-ceramic is greatly improved. The preparation comprises two ion exchange steps.)

1. The strengthened glass-ceramic with deep high compressive stress is characterized by comprising two corresponding compressive stress layers; the compressive stress layer extends inwards from the upper surface and the lower surface and sequentially comprises a surface compressive stress region and a deep layer compressive stress region; the total thickness of the surface compressive stress region and the deep compressive stress region is 50-100 um;

the thickness of the surface compressive stress region is 20um, and the stress CS of the surface compressive stress region is more than or equal to 800 MPa;

in the deep compressive stress region, the absolute value of the internal stress distribution slope is less than 2, CS-30 is more than or equal to 115MPa, and CS-50 is more than or equal to 80 MPa.

2. The strengthened glass-ceramic according to claim 1, wherein the thickness t, of the glass-ceramic is 0.55mm ≦ t < 0.8 mm; the thickness of the compressive stress layer is more than 0.2 t.

3. The strengthened glass ceramic as claimed in claim 2, wherein the thickness of the compressive stress layer is not less than 0.22 t.

4. The strengthened glass-ceramic according to claim 1, wherein the surface compressive stress zone stress CS is not less than 850 MPa.

5. The strengthened glass-ceramic according to claim 1, wherein CS-30 is 120MPa or more in the deep compressive stress region.

6. The strengthened glass-ceramic according to claim 1, wherein CS-50 is not less than 85MPa in the deep compressive stress region.

7. The strengthened glass-ceramic according to claim 1, wherein the strengthened glass-ceramic has a CT value of-50 to-90 MPa, a Vickers hardness of 6.50GPa or more, and a 4PB test value of 700N/mm or more²The loss rate of the single-rod static pressure strength is less than 10 percent, and the fracture threshold value is more than 5 kgf.

8. The method for preparing a strengthened glass-ceramic with deep high compressive stress as claimed in any one of claims 1 to 7, wherein the preparation of the glass-ceramic with deep high compressive stress comprises the following steps:

ion exchange for the first time: putting the basic microcrystalline glass into first bath salt for primary ion exchange, wherein the first bath salt comprises KNO₃And NaNO₃The molar ratio of Na/K in the first bath salt is 1.2-6.7: 1; the ion exchange temperature is higher than 480 ℃, and the exchange time is 3-6 h;

Secondary ion exchange: putting the basic microcrystalline glass subjected to the primary ion exchange into second bath salt for secondary ion exchange, wherein the second bath salt comprises 100 wt% of KNO₃Or in the mixture of potassium and sodium ions with the mole percentage content of sodium ions less than 10 percent; the secondary ion exchange temperature is 10-30 ℃ lower than the primary ion exchange temperature, and the exchange time is 0.5-2 h, so that the microcrystalline glass with deep high-pressure stress is obtained.

9. The method for preparing the strengthened glass-ceramic according to claim 8, wherein the base glass-ceramic has an average transmittance of > 89% at a wavelength range of 380-780 nm at a thickness of 0.75 mm.

10. The method for preparing the strengthened glass-ceramic according to claim 8, wherein the preparation of the basic glass-ceramic comprises the following steps:

preparing base glass: weighing and mixing the components according to the following mass percentage, and then melting, forming and annealing to obtain base glass;

SiO₂55 to 68 percent of Al₂O₃18 to 22 percent of Li₂4 to 7 percent of O and TiO₂0.5 to 1.8 percent of Na₂3 to 6 percent of O, 0 to 1 percent of alkaline earth metal oxide RO and B₂O₃0.5% -2% of P₂O₅1.5 to 4 percent of ZrO₂1 to 5 percent of clarifying agent and 0.15 to 0.4 percent of clarifying agent;

Wherein 21% < P₂O₅+Al₂O₃-RO＜24％、8％＜Li₂O+Na₂O≤11％，0.7％＜Li₂O/(Li₂O+TiO₂)＜1％；

Microcrystallization heat treatment: putting the base glass into a crystallization furnace, heating to Tg-Tg +30 ℃ at the speed of 8-12 ℃/min, preserving heat for 120-240 min, then heating to the crystallization temperature of 730-760 ℃ at the speed of 2-5 ℃/min, preserving heat for 60-120 min, then cooling to Tg-30-Tg-20 ℃ at the speed of 2-5 ℃/min, and preserving heat for 110-130 min; finally, reducing the temperature to 550-570 ℃ at the speed of 2 ℃/min, carrying out heat preservation treatment for 30min, and cooling to obtain the basic glass ceramics;

the content of the glass phase in the basic glass ceramics is 72 wt% -86 wt%, and the glass phase is composed of lithium aluminum silicate crystal grains with the average grain size less than 30 nm.

11. The method for preparing the strengthened microcrystalline glass according to claim 10, wherein the fining agent is SnO₂Or CeO₂One or a combination of both.

12. The method for preparing the strengthened glass-ceramic according to claim 10, wherein the Tg temperature is 624 ℃ to 655 ℃.

Technical Field

The invention relates to the field of microcrystalline glass, in particular to reinforced microcrystalline glass with deep high-pressure stress and a preparation method thereof.

Background

At present, a glass cover plate protection screen for a smart phone is upgraded from conventional one-step strengthening to lithium-aluminum-silicon secondary strengthening in order to improve the drop resistance. The lithium-aluminum-silicon secondary tempered glass contains lithium elements, can perform Na-Li (first step) and K-Na (second step) ion exchange, has high surface Compressive Stress (CS) and deeper stress layer (DOL), can improve the shock resistance of the glass to a certain extent, and particularly has good performance in resisting the impact of a flat object. However, it is easy to break in impact resistance against sharp objects, such as rough ground (cement, sand, etc.). While chemical strengthening may provide some resistance to crack penetration by penetrating the compressive stress layer at the surface of the glass or at a depth of the compressive stress layer, such resistance is relatively limited and is no longer effective once penetrating the compressive stress layer into the glass. Therefore, in order to better improve the impact resistance of the glass against sharp objects, not only high surface compressive stress and a deeper stress layer are required, but also a higher compressive stress value is required at a deep position.

The strengthening effect of the lithium-aluminum-silicon glass is influenced by the properties of the bulk glass and the strengthening process, the properties of the bulk glass determine the limit value of CT (central tensile stress), the actual value of CT is related to CS and DOL, when the CS and the DOL are increased, the CT is also increased, and when the actual CT value of the glass is close to or greater than the limit value of CT, the glass is cracked. The lithium aluminum silicon glass after secondary strengthening has larger CT value, and the glass is easy to crack in the strengthening experiment for improving the deep compressive stress value. Currently, the method for increasing the deep compressive stress is low-temperature long-time ion exchange, which takes a long time and increases the production cost. Alternatively, the exchange time may be reduced by increasing the diffusion rate by increasing the annealing temperature, but the applicable temperature may not be too high due to the stress relaxation phenomenon. Therefore, the effect of increasing the ion entering depth by increasing the strengthening temperature is limited, and the deep compressive stress is difficult to be improved, so that the anti-falling performance of the lithium-aluminum-silicon chemically strengthened glass is restricted.

Disclosure of Invention

Therefore, in order to solve the problems, the inventor introduces microcrystal particles into the lithium-aluminum-silicon glass, and the microcrystal particles have higher network structure strength than glass due to the fact that the microcrystal particles have a crystal phase, so that the toughness of the glass can be improved, and the maximum CT accommodation degree is improved; meanwhile, the microcrystal particles are stable at high temperature, and the stress relaxation amount can be reduced. The inventor utilizes the particularity of the microcrystalline particle structure, introduces a microcrystalline phase with a certain content into the lithium-aluminum-silicon glass through a certain formula design and a heat treatment process, and performs ion exchange under the limited chemical strengthening process condition to improve the compression stress value of the deep layer inside the microcrystalline glass product, so as to obtain the microcrystalline glass product with a high compression stress value at the deep layer inside.

To achieve the above object, in a first aspect of the present invention, there is provided a strengthened glass-ceramic having a deep layer high compressive stress, the strengthened glass-ceramic article comprising two corresponding compressive stress layers; the compressive stress layer extends inwards from the upper surface and the lower surface and sequentially comprises a surface compressive stress region and a deep layer compressive stress region; the total thickness of the surface compressive stress region and the deep compressive stress region is 50-100 um; the thickness of the surface compressive stress region is 0-20 um, and the stress CS of the surface compressive stress region is more than or equal to 800 MPa; in the deep compressive stress region, the absolute value of the internal stress distribution slope is less than 2, CS-30 is more than or equal to 115MPa, and CS-50 is more than or equal to 80 MPa.

Preferably, the thickness t of the microcrystalline glass is more than or equal to 0.55mm and less than 0.8 mm; the thickness of the compressive stress layer is more than 0.2 t.

Preferably, the thickness of the compressive stress layer is more than or equal to 0.22 t.

Preferably, the stress CS of the surface compressive stress area is more than or equal to 850 MPa.

Preferably, in the deep layer compression stress area, CS-30 is more than or equal to 120MPa,

preferably, CS-50 is more than or equal to 85MPa in the deep layer compression stress area.

Preferably, the CT value of the strengthened glass ceramics is-50 to-90 MPa, the Vickers hardness is more than or equal to 6.50GPa, and the 4PB test value is more than 700N/mm²The single-rod static pressure strength loss rate of the reinforced glass-ceramic is less than 10 percent, and the fracture threshold value is more than 5 kgf.

In order to achieve the above object, in a second aspect of the present invention, the present invention provides a method for preparing a strengthened glass-ceramic with deep high compressive stress according to the first aspect of the present invention, comprising the steps of:

first ion exchange (IOX): putting the basic microcrystalline glass into first bath salt for primary ion exchange, wherein the first bath salt comprises KNO₃And NaNO₃The molar ratio of Na/K in the first bath salt is 1.2-6.7: 1; the ion exchange temperature is higher than 480 ℃, and the exchange time is 3-6 h;

secondary ion exchange (IOX): putting the basic microcrystalline glass subjected to the primary ion exchange into second bath salt for secondary ion exchange, wherein the second bath salt comprises 100 wt% of KNO ₃Or in the mixture of potassium and sodium ions with the mole percentage content of sodium ions less than 10 percent; the secondary ion exchange temperature is 10-30 ℃ lower than the primary ion exchange temperature, and the exchange time is 0.5-2 h, so that the microcrystalline glass with deep high-pressure stress is obtained.

In the first ion exchange, in order to ensure the strengthening effect, the Na/K molar ratio is limited; the high potassium content is easy to accumulate on the shallow surface layer of the glass, so that the continuous entry of subsequent ions is not facilitated, and the depth of a stress layer is influenced; the excessive sodium content is beneficial to Na-Li exchange to a certain extent, improves the depth and deep layer compressive stress, but simultaneously forms a sodium-rich layer on the surface layer to influence the chemical stability of the glass. Therefore, the molar ratio of Na/K is limited to be 1.2-6.7 by the salt proportion of the ion exchange bath; the ion exchange temperature is higher than 480 ℃, the exchange temperature in some embodiments is higher than 530 ℃, and the effective exchange time is 3-6 h.

Preferably, the average transmittance of the base glass ceramics at a light wavelength range of 380-780 nm in thickness of 0.75mm is more than 89%;

preferably, the preparation of the basic glass ceramics comprises the following steps:

preparing base glass: weighing and mixing the components according to the following mass percentage, and then melting, forming and annealing to obtain base glass;

SiO₂55 to 68 percent of Al₂O₃18 to 22 percent of Li₂4 to 7 percent of O and TiO₂0.5 to 1.8 percent of Na₂3 to 6 percent of O, 0 to 1 percent of alkaline earth metal oxide RO and B₂O₃0.5% -2% of P₂O₅1.5 to 4 percent of ZrO₂1 to 5 percent of clarifying agent and 0.15 to 0.4 percent of clarifying agent;

wherein 21% < P₂O₅+Al₂O₃-RO＜24％、8％＜Li₂O+Na₂O≤11％，0.7％＜Li₂O/(Li₂O+TiO₂)＜1％；

SiO₂Constitutes the main structure of the base glass and the glass ceramics, and is also the main component constituting the crystal phase. Too low a content thereof may result in a change in the composition of the crystal phase and also may deteriorate the overall properties of the glass. SiO 2₂The content should not be less than 55 wt%. But higher SiO₂The content of the components can cause difficulty in melting and forming, and the components also contain high aluminum and zirconium components. Comprehensively considering: the invention uses SiO₂The content of (A) is controlled between 55 wt% and 68 wt%.

Al₂O₃Since the volume of the glass structure is larger than the volume of the silicon-oxygen tetrahedron, the glass can be provided with strengthening channels in the ion strengthening process, and the higher the content of the strengthening channels, the higher the content of the strengthening channels can promote the ion strengthening of the glass. The content thereof should not be less than 18 wt%; however, Al₂O₃Belongs to refractory oxide, can quickly improve the high-temperature viscosity of glass, increases the difficulty of clarification and homogenization of the glass, is not easy to discharge bubble defects, and controls the content of the bubble defects to be lower than 22 wt%.

Li₂O can reduce the crystallization temperature of the glass, promote the crystallization of the glass, is also a main component for ion exchange and improving the depth and strength of deep stress. To obtain better deep layer stress, Li ₂The O content should not be less than 4 wt.%. But too high Li₂O is very easy to crystallize, so that glass crystallization is difficult to control, the lithium cost is high, and the production cost is increased. Therefore, control of Li in the base glass₂The O content is not higher than 7 wt%.

TiO₂Is a nucleating agent, and can facilitate nucleation and formation and growth of crystal grains. It may be reacted with Li₂The combined action of O lowers the crystallization temperature. Taking into account Li in the composition₂O content, TiO thereof₂The components are controlled to be 0.5 to 1.8 percent.

Na₂O can significantly reduce the viscosity of the base glass, facilitating melting and fining of the base glass. Meanwhile, Na ions are also a major participant in ion exchange. Too low Na ion content is not favorable for ion exchange. But Na₂The increase of the O content causes the change of the kind of the crystalline phase, and generates a plurality of crystals with different properties, so that the crystallization process is difficult to control, and the glass is easy to devitrify or be uneven. Therefore, from the viewpoint of ion exchange, K is allowed to proceed in the latter stage of the glass ceramics⁺With Na⁺Ion exchange to form a high compressive stress on the surface of the glass, a minimum content of not less than 3 wt%, Na in the base glass from the viewpoint of control of the crystal phase₂The O content is not preferably higher than 6 wt%.

In certain embodiments, the alkaline earth metal oxide RO, R is present ²⁺May be Mg²⁺、Ca²⁺、Zn²⁺Or Ba²⁺It can improve the chemical stability and mechanical strength of the glass. But R is²⁺The ion diffusion rate is influenced, the influence is more obvious when the diameter of the ion diffusion rate is larger, and meanwhile, the larger ion radius has a certain blocking effect on an alkali ion channel. Therefore, the content of RO component is set to 0 wt% to 1 wt%. Mg having a smaller ion diameter is more preferable²⁺Or Zn²⁺。

B₂O₃Belongs to network forming body oxide, can reduce the high-temperature melting viscosity of the glass and improve the melting characteristic.It is suitable for improving ion diffusivity and improving ion exchange capacity. But B₂O₃Can cause phase separation, and can affect the transmittance of the crystallized glass along with the increase of the content, and the over-high content can also damage the main body network structure and reduce the mechanical strength. Thus, B₂O₃The content of the components is set to be 0.5 wt% -2 wt%.

P₂O₅One of the network former components belonging to the base glass is represented by [ PO4 ]]The tetrahedrons are connected with each other to form a network, so that the glass network structure is in a loose state, and the network gaps are enlarged, thereby being beneficial to the mutual diffusion of ions. Thus, P₂O₅The content is at least 1.5 wt%. But P is₂O₅Too high content can cause severe phase separation of the glass and affect the permeability of the glass ceramics, P₂O₅The content is at most 4 wt%.

ZrO₂The method is beneficial to reducing the size of crystal grains in the crystallization process, thereby improving the transmittance of the glass and rapidly improving the chemical stability and certain toughening effect of the glass. In this composition, Zr0 ₂Contribute to the stability of the main crystalline phase; if no Zr0₂The main crystal phase is easy to generate crystal form transformation, and the integral uniformity and permeability of the glass are affected. Thus, ZrO₂The minimum content of the components is not less than 1 wt%. But ZrO₂Belongs to a refractory component, can quickly improve the viscosity of base glass and has overhigh ZrO content₂The content may result in ZrO in the glass₂An unmelted mass is present. Thus, ZrO₂The content is controlled at most to 5 wt%.

Besides the oxides, the glass contains a chemical clarifying agent, and the clarifying agent can be decomposed at high temperature in the glass melting process, gasified to generate gas or reduce the viscosity of glass liquid, so that bubbles in the glass liquid are eliminated or dissolved and absorbed, and a better melting effect is achieved. In the present invention, the clarifier contains no Sb₂O₃CeO may be preferred₂And SnO₂The content of the clarifying agent is controlled to be 0.15-0.4%.

In particular, the invention limits the proportion of P to 21% < P to take account of the rapid diffusion and crystallization characteristics of ions₂O₅+Al₂O₃-RO＜24％、8％＜R₂O(Li₂O+Na₂O)≤11％，0.7％＜Li₂O/Li₂O+TiO₂＜1％。

Microcrystallization heat treatment: putting the base glass into a crystallization furnace, heating to a nucleation temperature Tg-Tg +30 ℃ at the speed of 8-12 ℃/min, preserving heat for 120-240 min, then heating to a crystallization temperature 730-760 ℃ at the speed of 2-5 ℃/min, preserving heat for 60-120 min, then cooling to a temperature Tg-30-Tg-20 ℃ at the speed of 2-5 ℃/min, and preserving heat for 110-130 min; and finally, reducing the temperature to 550-570 ℃ at the speed of 2 ℃/min, carrying out heat preservation treatment for 30min, and cooling to obtain the basic glass ceramics.

The content of the glass phase in the basic glass ceramics is 72 wt% -86 wt%, and the glass phase is composed of lithium aluminum silicate crystal grains with the average grain size less than 30 nm.

Preferably, the fining agent is SnO₂Or CeO₂One or a combination of both.

Preferably, the Tg is from 624 ℃ to 655 ℃.

Compared with the prior art, the invention at least comprises the following beneficial effects: a microcrystalline glass product with deep high compressive stress is provided, which can realize high compressive stress at the deep layer of the glass product under the condition of high temperature and high strength by introducing microcrystalline phase particles, and does not generate stress relaxation and cracking phenomena. The glass product has a surface compressive stress zone CS of more than 800MPa, an absolute value of an internal stress distribution slope of an internal deep layer (20-100um) region of less than 2, a high compressive stress value of more than or equal to 115MPa for CS-30 and more than or equal to 80MPa for CS-50 within the range that t is more than or equal to 0.55mm and less than or equal to 0.8mm in thickness; the DOC depth of the stress layer is more than 0.2 times of the thickness of the glass; the CT value is between 50 and 90MPa, the Vickers hardness is more than 6.50GPa, and the 4PB test value is more than 700N/mm²The loss rate of the single-rod static pressure strength is less than 10 percent, (prefabricated defects under 500kgf/15 s), the fracture threshold value is more than 5kgf, and the related performance of the reinforced glass-ceramic is greatly improved.

Drawings

FIG. 1 is a schematic longitudinal sectional view of a sample of examples 1 to 6;

FIG. 2 is a deep level stress curve of the sample of example 2;

FIG. 3 is a Scanning Electron Microscope (SEM) image of a sample of example 2;

FIG. 4 is a graph of the transmittance from 300nm to 1200nm wavelength for the sample of example 2;

FIG. 5 is a graph of the indentation of the sample of example 2 at a Vickers hardness of 5kgf/15 s;

FIG. 6 is an XRD pattern of a sample of example 2;

FIG. 7 is a graph of the deep layer stress distribution of the samples of examples 1-6;

FIG. 8 is a box plot of the samples of examples 1-6 at deep stresses of 30um and 50um versus the commercially superior amorphous secondary tempered glass.

Detailed Description

To explain technical contents, structural features, achieved objects and effects of the technical solutions in detail, the following detailed description is given in conjunction with the accompanying drawings 1 to 8 of the specification.

Examples 1 to 6 of the present invention were prepared by the following method:

1. weighing and mixing the components: selecting corresponding introduced raw material SiO according to the proportion of each component₂55 to 68 percent of Al₂O₃18 to 22 percent of Li₂4 to 7 percent of O and TiO₂0.5 to 1.8 percent of Na₂3 to 6 percent of O, 0 to 1 percent of alkaline earth metal oxide RO and B₂O₃0.5% -2% of P₂O₅1.5 to 4 percent of ZrO₂1 to 5 percent of clarifying agent and 0.15 to 0.4 percent of clarifying agent; wherein 21% < P ₂O₅+Al₂O₃-RO＜24％、8％＜Li₂O+Na₂O≤11％，0.7％＜Li₂O/(Li₂O+TiO₂) Less than 1 percent; weighing according to the purity, moisture and proportion range, and uniformly mixing to obtain a meltable mixture. The components and the mass percentages in examples 1-6 are shown in Table 1.

2. Preparing a base glass block:

putting the uniform mixture into a crucible made of platinum or platinum-rhodium, melting for 4-6 hours in an electric furnace at the temperature of 1600-1650 ℃ according to the melting difficulty of glass composition, stirring for 2-3 times to make the mixture uniform, cooling to a proper temperature, casting into a mold, putting the cast and molded glass block into an annealing furnace at the temperature of 600-650 ℃ for annealing, cooling to normal temperature along with the furnace after annealing, and taking out to obtain a base glass block.

3. Microcrystallization heat treatment:

putting the basic glass block into a crystallization furnace, and carrying out heat treatment in four stages; the heat treatment process parameters are shown in table 1, wherein the temperature is increased at 8-12 ℃/min in the first stage, the temperature is increased at 2-5 ℃/min in the second stage, the temperature is reduced at 1-2 ℃/min in the third stage, the temperature is reduced at 2 ℃/min in the fourth stage, furnace cooling is carried out after heat treatment, and the basic glass ceramics are taken out.

4. Preparing the reinforced glass ceramics:

and cutting, grinding and polishing the basic microcrystalline glass block to prepare the flaky glass. Ion exchange is carried out by adopting a two-step method. The method comprises the following steps: and (3) placing the sheet sample in a preheating furnace at 450 ℃ for heat preservation for 30min, then placing the basic glass ceramics 2 times into molten salt for ion strengthening (1IOX and 2IOX), wherein the ion strengthening process parameters are shown in table 1, and after the ion strengthening process parameters are finished, placing the glass in a muffle furnace for rapid cooling.

The test was performed by cleaning the surface residues of the base glass block and the chemically strengthened glass with hot water, and the results are shown in table 1 below and fig. 1-8.

Table 1 examples 1-6 sample compositions, process parameters and performance tables